Phosphonate nucleosides useful as active ingredients in pharmaceutical compositions for the treatment of viral infections, and intermediates for their production

ABSTRACT

The invention is directed to processes of preparing phosphonate nucleosides comprising a phosphonalkoxy-substituted five-membered, saturated or unsaturated, oxygen-containing ring coupled to a heterocyclic nucleobase such as a pyrimidine or purine base. These compounds can be described by general formula (II)

FIELD OF THE INVENTION

The present invention relates to a series of novel phosphonatenucleosides and thiophosphonate nucleosides, more specificallyphosphonate nucleosides and thiophosphonate nucleosides comprising aphosphonalkoxy-substituted or phosphonothioalkyl-substitutedfive-membered, saturated or unsaturated, oxygen-containing orsulfur-containing ring coupled to a heterocyclic nucleobase such as apyrimidine or purine base. The invention further relates to certainphosphonate nucleosides and thiophosphonate nucleosides having antiviralactivity, more specifically HIV (Human Immunodeficiency Virus)replication inhibiting properties. The invention also relates to methodsfor the preparation of such phosphonate nucleosides and thiophosphonatenucleosides, as well as novel intermediates useful in one or more stepsof such syntheses. The invention also relates to pharmaceuticalcompositions comprising an effective amount of such phosphonatenucleosides and thiophosphonate nucleosides as active ingredients. Thisinvention further relates to the use of such phosphonate nucleosides andthiophosphonate nucleosides as medicines or in the manufacture of amedicament useful for the treatment of mammals suffering from viralinfections, in particular HIV infection. This invention further relatesto methods for the treatment of viral infections in mammals by theadministration of a therapeutical amount of such phosphonate nucleosidesand thiophosphonate nucleosides, optionally combined with one or moreother drugs having anti-viral activity.

BACKGROUND OF THE INVENTION

A retrovirus designated human immunodeficiency virus (HIV) is theetiological agent of the complex disease that includes progressivedestruction of the immune system (acquired immune deficiency syndrome,hereinafter AIDS) and degeneration of the central and peripheral nervoussystem. There are two types of HIV, HIV-1 and HIV-2, the latterproducing a less severe disease than the former. Being a retrovirus, itsgenetic material is in the form of RNA (ribonucleic acid) consisting oftwo single RNA strands. Coexisting with RNA are reverse transcriptase(having polymerase and ribonuclease activity), integrase, a protease andother proteins.

It is known in the art that some antiviral compounds which act asinhibitors of HIV replication are effective agents in the treatment ofAIDS and similar diseases. Drugs that are known and approved for thetreatment of HIV-infected patients belong to one of the followingclasses:

-   -   nucleoside reverse transcriptase inhibitors (NRTI) such as, but        not limited to, azidothymidine, zidovudine, lamivudine,        didanosine, abacavir, adefovir and the like,    -   nucleotide reverse transcriptase inhibitors (NtRTI) such as, but        not limited to, tenofovir (commercially available under the        trade name Viread),    -   non-nucleoside reverse transcriptase inhibitors such as, but not        limited to, nevirapine, efavirenz and the like,    -   protease inhibitors such as, but not limited to, nelfinavir,        saquinavir, ritonavir, indinavir, amprenavir, fosamprenavir and        the like, and    -   fusion inhihitors such as enfuvirtide.

A relatively new target that was focused on lately is the integraseenzyme of HIV, while also many other proteins acting as enzymes orco-factors are being investigated.

Replication of the human immunodeficiency virus type 1 (hereinafterreferred as HIV-1) can be drastically reduced in infected patients bycombining potent antiviral drugs targeted at multiple viral targets, asreviewed by Vandamme et al. in Antiviral Chem. Chemother. (1998)9:187-203.

Multiple-drug combination regimes can reduce viral load below thedetection limit of the most sensitive tests. Nevertheless low levelongoing replication has been shown to occur, possibly in sanctuarysites, leading to the emergence of drug-resistant strains, according toPerelson et al. in Nature (1997) 387:123-124.

Furthermore the selectivity of many antiviral agents is rather low,possibly making them responsible for side-effects and toxicity.Moreover, HIV can develop resistance to most, if not all, currentlyapproved antiviral drugs, according to Schmit et al. in J. Infect. Dis.(1996) 174:962-968. It is well documented that the ability of HIV torapidly evolve drug resistance, together with toxicity problemsresulting from known drugs, requires the development of additionalclasses of antiviral drugs.

As a summary, there is still a stringent need in the art for potentinhibitors of HIV. Therefore a goal of the present invention is tosatisfy this urgent need by identifying efficient pharmaceuticallyactive ingredients that are less toxic and/or more resistant to virusmutations than existing antiviral drugs and that can be useful, eitheralone or in combination with other active ingredients, for the treatmentof retroviral infections, in particular lentiviral infections, and moreparticularly HIV infections, in mammals and more specifically in humans.Furthermore, another goal of the present invention is complementexisting antiviral drugs in such a way that the resulting drugcombination has improved activity or improved resistance to virusmutation than each of the individual compounds.

The family of the Flaviviridae consists of 3 genera, the pestiviruses,the flaviviruses and the hepaciviruses and also contains the hepatitis Gvirus (HGV/GBV-C) that has not yet been assigned to a genus.Pestiviruses such as the Classical Swine Fever Virus (CSFV), the BovineViral Diarrhea Virus (BVDV) and the Border Disease Virus (BDV) causeinfections of domestic livestock (respectively pigs, cattle and sheep)and are responsible for significant economic losses world-wide. Vaccinesare used in some countries with varying degrees of success to controlpestivirus disease. In other countries, animal culling and slaughter areused to contain pestivirus disease outbreaks.

The World Health Organization estimates that world-wide 170 millionpeople (3% of the world's population) are chronically infected with HCV.These chronic carriers are at risk of developing cirrhosis and/or livercancer. In studies with a 10 to 20 year follow-up, cirrhosis developedin 20-30% of the patients, 1 to 5% of whom may develop liver cancerduring the next then years. The only treatment option available today isthe use of interferon α-2 (or its pegylated from) either alone orcombined with ribavirin. However, sustained response is only observed inabout 40% of the patients and treatment is associated with seriousadverse effects. There is thus an urgent need for potent and selectiveinhibitors of the replication of the HCV in order to treat infectionswith HCV.

Furthermore, the study of specific inhibitors of HCV replication hasbeen hampered by the fact that it is not possible to propagate HCV(efficiently) in cell culture. Since HCV and pestiviruses belong to thesame virus family and share many similarities (organisation of thegenome, analogous gene products and replication cycle), pestiviruseshave been adopted as a model and surrogate for HCV. For example BVDV isclosely related to hepatitis C virus (HCV) and used as a surrogate virusin drug development for HCV infection.

In view of their important pharmacological value, there is a need fordrugs having antiviral activity against viruses belonging to the familyof Flaviviridae including hepatitis C virus.

Pioneering work on the chemistry of phosphonate nucleosides has alreadybeen carried out and includes certain important reaction schemes tosynthesize phosphonate nucleosides. A review of chemistry and biology ofphosphorous-modified nucleotide analogues is available for instance fromA. Holy in Advances in Antiviral Drug Design (1993) 1:179-231.Phosphonate nucleosides can be devided in two categories. A firstcategory are real nucleoside analogues since they contain a nucleobaseand a sugar moiety. A second category of phosphonate nucleosides,represented for instance by 9-(2-phosphonyl-methoxyethyl)adenine(adefovir), can be considered as alkylated nucleobases since their sugarmoiety is replaced by an alkoxyalkyl moiety. Surprisingly, up to now,potent antiviral in vivo activity (HSV, CMV, HBV, HIV) has only beenassociated with certain phosphonalkoxyalkyl nucleobases and not withsugar containing phosphonate nucleosides. Several attempts to discoverantiviral nucleoside phosphonates have led to synthetic schemes for thepreparation of furanose-, pyranose- and carbocyclic phosphonatenucleosides, all of them however lacking potent antiviral activity.

Phosphorylation by kinases and incorporation into nucleic acids(eventually leading to chain termination) is considered as an importantmechanism which may explain the antiviral activity of nucleosides. Thelack of antiviral activity of phosphonate nucleosides of the firstcategory is generally explained by their poor substrate properties forcellular and viral kinases. On the other hand, the potent antiviralactivity of phosphonylated alkylated nucleobases of the second categoryhas been ascribed to their intracellular phosphorylation intodiphosphates and to an incorporation of the modified nucleosides intonucleic acids (enzymatic incorporation into nucleic acids being almostirreversible) which has negative consequences downstream and therebyinhibits viral growth. A disadvantage of the acyclic nucleosidephosphonates are their low selectivity index in cellular screeningsystems. The selectivity of the triphosphates of anti-HIV nucleosidesfor HIV reverse transcriptase versus mitochondrial DNA polymerases isusually regarded as an important factor determining in vivo toxicity.Thus there is still a need in the art for drug candidates havingsuitable selectivity for HIV reverse transcriptase. A less flexiblestructure such as is present in the nucleosides phosphonates isconsidered to improve both binding to polymerases and viral-versus-hostselectivity. Consequently, nucleosides phosphonates retaining their HIVreverse transcriptase affinity are considered as strong antiviralcandidates.

Threose nucleosides have been previously synthesized because they can beassembled from natural precursor molecules. It has been demonstratedthat threose nucleic acids (TNA) form duplexes with DNA and RNAexhibiting a thermal stability similar to that of the natural nucleicacids association. Triphosphates of threose nucleosides are accepted assubstrate by several polymerases and can be enzymatically incorporatedin DNA. A few 2,5-dihydro-5-(phosphonomethoxy)-2-furanyl nucleosidesderived from thymine and adenine with antiretroviral activity have beendisclosed by Kim et al. in J. Org. Chem. (1991) 56:2642-2647.EP-A-398,231 describes a family of phosphonomethoxy-methoxymethylpurine/pyrimidine derivatives being effective in combating viralinfections at a dose of 0.01 to 30 mg/kg bodyweight. U.S. PatentPublication No. 2004/0023921 discloses a pharmaceutical compositioncomprising a nucleotide analog with a phosphonate group at an amounteffective to inhibit a viral polymerase of an hepatitis C virus(hereinafter referred as HCV) or to act as a substrate for the viralpolymerase of the HCV virus. WO 98/20017 describes a family of modifiednucleoside-5′-triphosphates which are inhibitors or substrates of DNApolymerases and antiviral agents, being in particular able to inhibitthe reproduction of the human HIV virus in a culture of humanlymphocytes.

Although, as is apparent from the prior art of record, numerouscompounds were proposed for meeting the various above mentionedrequirements in terms of retroviral therapy, it was observed that noneof them does achieve such goals and, consequently, there is still astringent need in the art for new compounds being able to solve theseproblems.

SUMMARY OF THE INVENTION

Without wishing to be bound by theory, the present invention is based onthe unexpected finding that the above-mentioned problems can be solvedby a novel class of compounds wherein the phosphonoalkoxy group orphosphonothioalkyl group of a furanose nucleoside phosphonate (or itssulfur analogue wherein furanyl is replaced with thienyl) is bound atthe 3′-position, thus bringing the phosphorous atom and the nucleobasemuch closer to each other than in the previously known nucleosidephosphonates. This invention is also based on the unexpected findingthat the absence of a hydroxymethyl substituent in the 4′-position ofthis class of compounds avoids steric hindrance during the enzymaticphosphorylation reaction, therefore avoiding the poor substrateproperties for cellular and viral kinases (leading to poor antiviralactivity) of the nucleoside phosphonates of the prior art. In addition,depending on the length of the carbon-based linking structure betweenthe 5-membered ring and the phosphorous atom, the phosphonylatednucleosides of the invention can be considered as mono-, di- ortriphosphate mimics. By varying the length of this linking structure,the present invention makes it possible to further finely tune theantiviral activity of the novel class of compounds. Also, this inventionis based on the unexpected finding that the presence of an anomericcentre in this novel class of threose nucleoside phosphonates providesthem with similar stereo-electronic properties to that of naturalnucleosides.

Based on the above unexpected findings, the present invention providesnew anti-viral agents, especially anti-retroviral agents, and moreparticularly anti-HIV compounds. These compounds are phosphonatenucleosides, more particularly phosphonoalkoxy-substituted andphosphonothioalkyl-substituted nucleosides comprising a five-membered,saturated or unsaturated, oxygen-containing or sulfur-containing ring(preferably dihydrofuranyl, tetrahydrofuranyl, dihydrothienyl ortetrahydrothienyl), or analogues or derivatives thereof, which have beenshown that they possess anti-viral activity against various classes ofviruses such as, but not limited to, retriviridae, flaviviridae andpapoviridae, more specifically against the human HIV. The presentinvention demonstrates that these compounds efficiently inhibit thereplication of HIV in mammals. Therefore, these phosphonate nucleosidesconstitute a useful class of new potent anti-viral compounds that can beused in the treatment and/or prevention of viral infections in animalssuch as mammals, and humans, more specifically for the treatment and/orprevention of HIV in humans.

The present invention also relates to compounds having antiviralactivities with respect to one or more other viruses such as, but notlimited to, hepatitis B virus, hepatitis C virus, papilloma virus,flaviviruses, picornaviruses and the like. The present inventionfurthermore relates to the use of such compounds as medicines, morespecifically as anti-viral agents, and to their use for the manufactureof medicaments for treating and/or preventing viral infections, inparticular retroviral infections such as, but not limited to, HIV inhumans. The invention also relates to methods for the preparation of allsuch compounds and to pharmaceutical compositions comprising them in ananti-viral effective amount.

The present invention also relates to a method of treatment orprevention of viral infections, in particular retroviral infections suchas, but not limited to, HIV in humans by the administration of one ormore such compounds, optionally in combination with one or more otheranti-viral agents, to a patient in need thereof.

One particularly useful aspect of the present invention is the provisionof new phosphonate nucleosides comprising a phosphonoalkoxy-substitutedor phosphonothioalkyl-substituted five-membered, saturated orunsaturated, ring which is coupled to a heterocyclic nucleobase,preferably a pyrimidine or a purine base. In another particularly usefulembodiment of the invention, the five-membered, saturated orunsaturated, ring is an oxygen-containing ring such as dihydrofuranyland tetrahydrofuranyl.

An embodiment of the invention relates to novel3′-phosphonalkoxy-substituted or 3′-phosphonothioalkyl-substituted,saturated or unsaturated, furanose nucleosides comprising a purine orpyrimidine base coupled to the 1′ position of a furanose, whereby the 3′position of the furanose is substituted with a phosphonoalkoxy group ora phosphonothioalkyl group. These nucleosides can also be derived fromtetrahydrofuran or 3,4-dihydrofuran thereby substituted at the 2position with a heterocyclic base such as, but not limited to,pyrimidine and purine bases, and at the 4 position with aphosphonoalkoxy group or phosphonothioalkyl group.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A, 1B, and 2-15 schematically show a number of alternativesynthetic routes for making various embodiments of the nucleosidephosphonates of this invention, as well as intermediates involved insuch synthetic routes. More specifically these synthetic routes relateto 2′ substitution and, still more specifically, to a differentstereochemistry at the 1′ and 3′ positions of the molecule.Abbreviations used in the figures are defined in the specificationherein after. In particular, “Nu” stands for a nucleophile.

DEFINITIONS

As used herein, and unless stated otherwise, the term “furanose” refersto five-membered cyclic monosaccharides and, by extension, to theirsulfur analogues. The numbering of monosaccharides starts at the carbonnext to the oxygen inclosed in the ring and is indicated with a prime(′).

As used herein, and unless stated otherwise, the term “phosphonalkoxy”refers to a phosphonate coupled via an alkylgroup (such as definedherein after) to an oxygen atom which itself can be coupled to anothermolecule or group.

As used herein, and unless stated otherwise, the term“phosphono-thioalkyl” refers to a phosphonate coupled via an alkylgroup(such as defined herein after) to a sulfur atom which itself can becoupled to another molecule or group.

As used herein, and unless stated otherwise, the term“3′-phosphono-alkoxy furanose nucleoside” refers to a heterocyclic base,such as a purine or pyrimidine base, coupled to the 1′ position of afuranose whereby the 3′ position of said furanose is substituted with aphosphonoalkoxy group.

As used herein, and unless stated otherwise, the terms “heterocyclicnucleobase” and “pyrimidine and purine bases” include, but are notlimited to, adenine, thymine, cytosine, uracyl, guanine and(2,6-)diaminopurine such as may be found in naturally-occurringnucleosides. The term also includes analogues and derivatives thereof.An analogue thereof is a base which mimics such naturally-occurringbases in such a way that its structure (the kinds of atoms present andtheir arrangement) is similar to the above-listed naturally-occurringbases but is modified by either having additional functional propertieswith respect to the naturally-occurring bases or lacking certainfunctional properties of the naturally-occurring bases. Such analoguesinclude, but are not limited to, those derived by replacement of a —CH—moiety by a nitrogen atom (e.g. 5-azapyrimidines such as 5-azacytosine)or vice-versa (e.g. 7-deazapurines, such as 7-deaza-adenine or7-deazaguanine) or both (e.g. 7-deaza, 8-azapurines). A derivative ofnaturally-occurring bases, or analogues thereof, is a compound whereinthe heterocyclic ring of such bases is substituted with one or moreconventional substituents independently selected from the groupconsisting of halogen, hydroxyl, amino and C₁₋₆ alkyl. Some additionalillustrative examples are provided in the specification herein after.Such purine or pyrimidine bases, analogues and derivatives thereof, arewell known to those skilled in the art, e.g. from documents such as, butnot limited to, WO 03/093290 and WO 04/028481.

As used herein, and unless stated otherwise, the term “alkyl” as usedherein refers to linear or branched saturated hydrocarbon chains havingfrom 1 to 18 carbon atoms such as, but not limited to, methyl, ethyl,1-propyl, 2-propyl, 1-butyl, 2-methyl-1-propyl (isopropyl), 2-butyl(sec-butyl), 2-methyl-2-propyl (tert-butyl), 1-pentyl, 2-pentyl,3-pentyl, 2-methyl-2-butyl, 3-methyl-2-butyl, 3-methyl-1-butyl,2-methyl-1-butyl, 1-hexyl, 2-hexyl, 3-hexyl, 2-methyl-2-pentyl,3-methyl-2-pentyl, 4-methyl-2-pentyl, 3-methyl-3-pentyl,2-methyl-3-pentyl, 2,3-dimethyl-2-butyl, 3,3-dimethyl-2-butyl, n-pentyl,n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl,n-tridecyl, n-tetradecyl, n-pentadecyl, n-hexadecyl, n-heptadecyl,n-octadecyl, and the like; preferably the alkyl group has from 1 to 8carbon atoms, more preferably from 1 to 4 carbon atoms.

As used herein, and unless stated otherwise, the term “cycloalkyl” meansa monocyclic saturated hydrocarbon monovalent radical having from 3 to10 carbon atoms, such as for instance cyclopropyl, cyclobutyl,cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl and the like, or aC₇₋₁₀ polycyclic saturated hydrocarbon monovalent radical having from 7to 10 carbon atoms such as, for instance, norbornyl, fenchyl,trimethyltricycloheptyl or adamantyl.

As used herein, and unless stated otherwise, the terms “alkenyl” and“cycloalkenyl” refer to linear or branched hydrocarbon chains havingfrom 2 to 18 carbon atoms, respectively cyclic hydrocarbon chains havingfrom 3 to 10 carbon atoms, with at least one ethylenic unsaturation(i.e. a carbon-carbon sp2 double bond) which may be in the cis or transconfiguration such as, but not limited to, vinyl (—CH═CH₂), allyl(—CH₂CH═CH₂), cyclopentenyl (—C₅H₇), and 5-hexenyl(—CH₂CH₂CH₂CH₂CH═CH₂).

As used herein, and unless stated otherwise, the terms “alkynyl” and“cycloalkynyl” refer to linear or branched hydrocarbon chains havingfrom 2 to 18 carbon atoms, respectively cyclic hydrocarbon chains havingfrom 3 to 10 carbon atoms, with at least one acetylenic unsaturation(i.e. a carbon-carbon sp triple bond) such as, but are not limited to,ethynyl (—C≡CH), propargyl (—CH₂C≡CH), cyclopropynyl, cyclobutynyl,cyclopentynyl, or cyclohexynyl.

As used herein with respect to a substituting radical, and unlessotherwise stated, the term “aryl” designates any mono- or polycyclicaromatic monovalent hydrocarbon radical having from 6 up to 30 carbonatoms such as but not limited to phenyl, naphthyl, anthracenyl,phenantracyl, fluoranthenyl, chrysenyl, pyrenyl, biphenylyl, terphenyl,picenyl, indenyl, biphenyl, indacenyl, benzocyclobutenyl,benzocyclooctenyl and the like, including fused benzo-C₄₋₈ cycloalkylradicals (the latter being as defined above) such as, for instance,indanyl, tetrahydronaphtyl, fluorenyl and the like, all of the saidradicals being optionally substituted with one or more substituentsindependently selected from the group consisting of halogen, amino,trifluoromethyl, hydroxyl, sulfhydryl and nitro, such as for instance4-fluorophenyl, 4-chlorophenyl, 3,4-dichlorophenyl, 4-cyanophenyl,2,6-dichlorophenyl, 2-fluorophenyl, 3-chlorophenyl, 3,5-dichlorophenyland the like.

As used herein with respect to a substituting group, and unlessotherwise stated, the terms “arylalkyl”, “arylalkenyl” and“heterocyclic-substituted alkyl” refer to an aliphatic saturated orethylenically unsaturated hydrocarbon monovalent group (preferably aC₁₋₁₈ alkyl or C₂₋₁₈ alkenyl such as defined above) onto which an arylor heterocyclic group (such as defined herein) is already bonded, andwherein the said aliphatic group and/or the said aryl or heterocyclicgroup may be optionally substituted with one or more substituentsindependently selected from the group consisting of halogen, amino,hydroxyl, sulfhydryl, C₁₋₇ alkyl, trifluoromethyl and nitro, such as butnot limited to benzyl, 4-chlorobenzyl, 4-fluorobenzyl, 2-fluorobenzyl,3,4-dichlorobenzyl, 2,6-dichlorobenzyl, 3-methylbenzyl, 4-methylbenzyl,4-ter-butylbenzyl, phenylpropyl, 1-naphthylmethyl, phenylethyl,1-amino-2-phenylethyl, 1-amino-2-[4-hydroxy-phenyl]ethyl,1-amino-2-[indol-2-yl]ethyl, styryl, pyridylmethyl (including allisomers thereof), pyridylethyl, 2-(2-pyridyl)isopropyl, oxazolylbutyl,2-thienylmethyl, pyrrolylethyl, morpholinyl-ethyl, imidazol-1-yl-ethyl,benzodioxolylmethyl and 2-furylmethyl.

As used herein with respect to a substituting group, and unlessotherwise stated, the term “heterocyclic ring” or “heterocyclic” means amono- or polycyclic, saturated or mono-unsaturated or polyunsaturatedmonovalent hydrocarbon group having from 3 up to 15 carbon atoms andincluding one or more heteroatoms in one or more heterocyclic rings,each of said rings having from 3 to 10 atoms (and optionally furtherincluding one or more heteroatoms attached to one or more carbon atomsof said ring, for instance in the form of a carbonyl or thiocarbonyl orselenocarbonyl group, and/or to one or more heteroatoms of said ring,for instance in the form of a sulfone, sulfoxide, N-oxide, phosphate,phosphonate or selenium oxide group), each of said heteroatoms beingindependently selected from the group consisting of nitrogen, oxygen,sulfur, selenium and phosphorus, also including radicals wherein aheterocyclic ring is fused to one or more aromatic hydrocarbon rings forinstance in the form of benzo-fused, dibenzo-fused and naphto-fusedheterocyclic radicals; within this definition are included heterocyclicgroups such as, but not limited to, pyridyl, dihydropyridyl,tetrahydropyridyl (piperidyl), thiazolyl, tetrahydrothienyl,tetrahydrothienyl sulfoxide, furanyl, thienyl, pyrrolyl, pyrazolyl,imidazolyl, tetrazolyl, benzofuranyl, thianaphthalenyl, indolyl,indolenyl, quinolinyl, isoquinolinyl, benzimidazolyl, piperidinyl,4-piperidonyl, pyrrolidinyl, 2-pyrrolidonyl, pyrrolinyl,tetrahydrofuranyl, bis-tetrahydrofuranyl, tetrahydropyranyl,bis-tetrahydropyranyl, tetrahydroquinolinyl, tetrahydroisoquinolinyl,decahydroquino-linyl, octahydroisoquinolinyl, azocinyl, triazinyl,6H-1,2,5-thiadiazinyl, 2H,6H-1,5,2-dithiazinyl, thianthrenyl, pyranyl,isobenzofuranyl, chromenyl, xanthenyl, phenoxathinyl, 2H-pyrrolyl,isothiazolyl, isoxazolyl, pyrazinyl, pyridazinyl, indolizinyl,isoindolyl, 3H-indolyl, 1H-indazoly, purinyl, 4H-quinolizinyl,phthalazinyl, naphthyridinyl, quinoxalinyl, quinazolinyl, cinnolinyl,pteridinyl, 4aH-carbazolyl, carbazolyl, β-carbolinyl, phenanthridinyl,acridinyl, pyrimidinyl, phenanthrolinyl, phenazinyl, phenothiazinyl,furazanyl, phenoxazinyl, isochromanyl, chromanyl, imidazolidinyl,imidazolinyl, pyrazolidinyl, pyrazolinyl, piperazinyl, indolinyl,isoindolinyl, quinuclidinyl, morpholinyl, oxazolidinyl, benzotriazolyl,benzisoxazolyl, oxindolyl, benzoxazolinyl, benzothienyl, benzothiazolyland isatinoyl; heterocyclic groups may be sub-divided intoheteroaromatic (or “heteroaryl”) groups such as, but not limited to,pyridyl, dihydropyridyl, pyridazinyl, pyrimidinyl, pyrazinyl,s-triazinyl, oxazolyl, imidazolyl, thiazolyl, isoxazolyl, pyrazolyl,isothiazolyl, furanyl, thiofuranyl, thienyl, and pyrrolyl, andnon-aromatic heterocyclic groups; when a heteroatom of the saidnon-aromatic heterocyclic group is nitrogen, the latter may besubstituted with a substituent selected from the group consisting ofalkyl, cycloalkyl, aryl, arylalkyl and alkylaryl (suchb as definedherein); by way of example, carbon-bonded heterocyclic rings may bebonded at position 2, 3, 4, 5, or 6 of a pyridine, at position 3, 4, 5,or 6 of a pyridazine, at position 2, 4, 5, or 6 of a pyrimidine, atposition 2, 3, 5, or 6 of a pyrazine, at position 2, 3, 4, or 5 of afuran, tetrahydrofuran, thiofuran, thiophene, pyrrole ortetrahydropyrrole, at position 2, 4, or 5 of an oxazole, imidazole orthiazole, at position 3, 4, or 5 of an isoxazole, pyrazole, orisothiazole, at position 2 or 3 of an aziridine, at position 2, 3, or 4of an azetidine, at position 2, 3, 4, 5, 6, 7, or 8 of a quinoline or atposition 1, 3, 4, 5, 6, 7, or 8 of an isoquinoline; still more specificcarbon-bonded heterocycles include 2-pyridyl, 3-pyridyl, 4-pyridyl,5-pyridyl, 6-pyridyl, 3-pyridazinyl, 4-pyridazinyl, 5-pyridazinyl,6-pyridazinyl, 2-pyrimidinyl, 4-pyrimidinyl, 5-pyrimidinyl,6-pyrimidinyl, 2-pyrazinyl, 3-pyrazinyl, 5-pyrazinyl, 6-pyrazinyl,2-thiazolyl, 4-thiazolyl, or 5-thiazolyl; by way of example,nitrogen-bonded heterocyclic rings may be bonded at position 1 of anaziridine, azetidine, pyrrole, pyrrolidine, 2-pyrroline, 3-pyrroline,imidazole, imidazolidine, 2-imidazoline, 3-imidazoline, pyrazole,pyrazoline, 2-pyrazoline, 3-pyrazoline, piperidine, piperazine, indole,indoline, 1H-indazole, at position 2 of an isoindole or isoindoline, atposition 4 of a morpholine, and at position 9 of a carbazole orβ-carboline, still more specific nitrogen-bonded heterocycles include1-aziridyl, 1-azetedyl, 1-pyrrolyl, 1-imidazolyl, 1-pyrazolyl and1-piperidinyl.

The term “acyl” as used herein, unless otherwise stated, refers to acarbonyl group directly attached to an alkyl, alkenyl, alkynyl, aryl,heterocyclic, arylalkyl, arylalkenyl, arylalkynyl, heterocyclic-alkyl,heterocyclic-alkenyl or heterocyclic-alkynyl group, such as for examplealkanoyl (alkylcarbonyl), aroyl (arylcarbonyl), arylalkanoyl oralkylaroyl group, wherein the carbonyl group is coupled to anothermolecule. As an example, the term “acyloxyalkyl” refers to an acyl groupcoupled via an oxygen atom to an alkyl group, the latter being furthercoupled to another molecule or atom.

As an example, “alkylalkenylcarbonate” refers to a alkyl-OC(O)O-alkenylgroup, thus a carbonate substituted at one side with an alkyl and on theother side with an alkenyl, one of the alkyl and alkenyl groups beingfurther coupled to another molecule or atom.

As used herein and unless otherwise stated, the terms “alkoxy”,“cyclo-alkoxy”, “aryloxy”, “arylalkyloxy”, “oxyheterocyclic”,“thioalkyl”, “thio cycloalkyl”, “arylthio”, “arylalkylthio” and“thioheterocyclic” refer to substituents wherein an alkyl group,respectively a cycloalkyl, aryl, arylalkyl or heterocyclic group (eachof them such as defined herein), are attached to an oxygen atom or asulfur atom through a single bond, such as but not limited to methoxy,ethoxy, propoxy, butoxy, thioethyl, thiomethyl, phenyloxy, benzyloxy,mercaptobenzyl and the like.

As used herein and unless otherwise stated, the term halogen means anyatom selected from the group consisting of fluorine, chlorine, bromineand iodine.

As used herein with respect to a substituting radical, and unlessotherwise stated, the term “amino-acid” refers to a radical derived froma molecule having the chemical formula H₂N—CHR—COOH, wherein R is theside group of atoms characterizing the amino-acid type; said moleculemay be one of the 20 naturally-occurring amino-acids or any similar nonnaturally-occurring amino-acid.

As used herein and unless otherwise stated, the term “stereoisomer”refers to all possible different isomeric as well as conformationalforms which the compounds of the invention may possess, in particularall possible stereochemically and conformationally isomeric forms, alldiastereomers, enantiomers and/or conformers of the basic molecularstructure. Some compounds of the present invention may exist indifferent tautomeric forms, all of the latter being included within thescope of the present invention.

As used herein and unless otherwise stated, the term “enantiomer” meanseach individual optically active form of a compound of the invention,having an optical purity or enantiomeric excess (as determined bymethods standard in the art) of at least 80% (i.e. at least 90% of oneenantiomer and at most 10% of the other enantiomer), preferably at least90% and more preferably at least 98%.

As used herein and unless otherwise stated, the term “solvate” includesany combination which may be formed by a compound of this invention witha suitable inorganic solvent (e.g. hydrates) or organic solvent, such asbut not limited to alcohols, ketones, esters and the like.

The term “pharmaceutically acceptable carrier or excipient” as usedherein refers to any material or substance with which the activeprinciple, i.e. a compound of this invention may be formulated in orderto facilitate its application or dissemination to the locus to betreated, for instance by dissolving, dispersing or diffusing the saidcomposition, and/or to facilitate its storage, transport or handlingwithout impairing its effectiveness. The pharmaceutically acceptablecarrier may be a solid or a liquid or a gas which has been compressed toform a liquid.

As used herein and unless otherwise stated, the term “tetrose” refers toany of a class of monosaccharides containing four carbon atoms such as,but not limited to, erythrose or threose with the general formulaC₄H₈O₄. Tetrose compounds (carbohydrate nomenclature) can alternativelybe named as tetrahydrofuranyl compounds (IUPAC nomenclature) since theyshare the five-membered oxygen-containing heterocycle.

As used herein and unless otherwise stated, the term “anomeric carbon”refers to the carbon atom containing the carbonyl functionality of asugar molecule, also referred to as a carbohydrate. This carbon atom isinvolved in the hemiacetal or hemiketal formation characteristic for thesugar ring structure. This carbonyl carbon is referred to as theanomeric carbon because it is non-chiral in the linear structure, andchiral in the cyclic structure.

As used herein and unless otherwise stated, the term “selectiveprotection” and “selective deprotection” refers to the introduction,respectively the removal, of a protecting group on a specific reactivefunctionality in a molecule containing several functionalities,respectively containing several protected functionalities, and leavingthe rest of the molecule unchanged. Many molecules used in the presentinvention contain more than one reactive functionality. For examplecarbohydrates are characterised by more than one alcohol functionalgroup. It is often necessary to manipulate only one (or some) of thesegroups at a time without interfering with the other functionalities.This is only possible by choosing a variety of protecting groups, whichcan be manipulated using different reaction conditions. The use ofprotecting groups in such a way that it is possible to modify afunctionality independently from the other functionalities present inthe molecule is referred to as “orthogonal protection”. The developmentof orthogonal protecting group strategies makes it possible to removeone set of protecting groups in any order with reagents and conditions,which do not affect the groups in other sets. An efficient protectinggroup strategy can be critical for accomplishing the synthesis of large,complex molecules possessing a diverse range of reactive functionality.This protection reaction can be chemoselective when selectivity is dueto chemical properties, regioselective when due to the location of thefunctionality within the molecule. A reaction or transformation can be“stereoselective” in two ways, i.e. (1) because it will only occur at aspecific stereoisomer or at a specific stereo-orientation of thefunctionality, or (2) because it will result in only one specificstereoisomer. A protection reaction can therefore also bestereoselective for example in a way that it will only result inprotection of a functionality when in a certain conformation.

As used herein and unless otherwise stated, the snake-like symbol standsfor a bond with specific stereo-orientation but for which both optionsare possible, i.e. for any stereochemical arrangement of said bond.

DETAILED DESCRIPTION OF THE INVENTION

One embodiment of the present invention relates to novel compounds being3′-phosphonate substituted furanose nucleosides represented by thegeneral formula (I):

wherein:

-   -   B is a heterocycle selected from the group consisting of        pyrimidine and purine bases;    -   the snake-like symbol means any stereochemical arrangement of        the bond linking B, or the phosphonalkoxy group, to the furanyl        group.    -   R¹ and R² are each independently selected from the group        consisting of hydrogen; (—PO₃R¹⁶)_(m)—PO₃R¹⁷R¹⁸; alkyl; alkenyl;        alkynyl; cycloalkyl; cycloalkenyl; cycloalkynyl; aryl;        arylalkyl; heterocyclic ring; heterocyclic ring-alkyl;        acyloxyalkyl; acyloxyalkenyl; acyloxyalkynyl; acyloxyaryl;        acyloxyarylalkyl; acyloxyarylalkenyl; acyloxyarylalkynyl;        dialkylcarbonate; alkylarylcarbonate; alkylalkenylcarbonate;        alkylalkynylcarbonate; alkenylaryl-carbonate;        alkynylarylcarbonate; alkenylalkynylcarbonate;        dialkenylcarbonate; dialkynyl-carbonate; wherein said alkyl,        alkenyl and alkynyl can contain a heteroatom in or at the end of        the hydrocarbon chain, said heteroatom being selected from the        group consisting of oxygen, sulfur and nitrogen; and R¹ and R²        are further selected from substituents known for phosphonates        described as anti-viral agents;    -   R⁵ is selected from hydrogen, azido, halogen (preferably)        fluoro, cyano, alkyl, alkenyl, alkynyl, SR¹⁴ and OR¹⁴;    -   R¹⁴ is selected from hydrogen; alkyl; alkenyl; alkynyl;        cycloalkyl; cycloalkenyl; cycloalkynyl; aryl; heterocyclic ring;        arylalkyl; heterocyclic ring-alkyl; acyloxyalkyl; wherein said        alkyl, alkenyl and alkynyl can contain a heteroatom in or at the        end of the hydrocarbon chain, said heteroatom being selected        from the group consisting of oxygen, sulfur and nitrogen;    -   R¹⁶, R¹⁷ and R¹⁸ are independently selected from the group        consisting of hydrogen; alkyl; alkenyl; alkynyl; cycloalkyl;        cycloalkenyl; cycloalkynyl; aryl; arylalkyl; heterocyclic ring;        heterocyclic ring-alkyl; acyloxyalkyl; wherein said alkyl,        alkenyl and alkynyl can contain a heteroatom in or at the end of        the hydrocarbon chain, said heteroatom being selected from the        group consisting of oxygen, sulfur and nitrogen;    -   n is an integer selected from 1, 2, 3, 4, 5 or 6;    -   m is 0 or 1,        including pharmaceutically acceptable salts, solvates, and        isomers thereof.

In one embodiment, the invention relates to compounds according to thegeneral formula (I), wherein B is selected from adenine and thymine. Inanother particular embodiment, the 3′-phosphonalkoxy substituent or thepurine or pyrimidine base (i.e. the heterocycle B) coupled to the ringof the compounds according to the general formula (I) are in the R or Sconfiguration.

In its more general acceptance, the invention relates to a first classof compounds including a heterocyclic nucleobase attached to a firstcarbon atom of an optionally substituted five-member saturatedheterocyclic group selected from tetrahydrofuranyl and tetrahydrothienyland further including a phosphonoalkoxy, thiophosphonoalkoxy,phosphonothioalkyl or thiophosphonothioalkyl group attached to a secondcarbon atom of said five-member saturated heterocyclic group, said firstcarbon atom being adjacent to the heteroatom of said five-membersaturated heterocyclic group, and said second carbon atom being adjacentneither to the heteroatom nor to the first carbon atom of saidfive-member saturated heterocyclic group. This first class of compoundsmay be represented by the general formula (II):

wherein:

-   -   X¹, X², X³, X⁴ and X⁵ are each each independently selected from        the group consisting of oxygen and sulfur,    -   B is a natural or non-natural heterocyclic nucleobase,    -   R¹ and R² are each independently selected from the group        consisting of hydrogen; (—PO₃R¹⁶)_(m)—PO₃R¹⁷R¹⁸; alkyl; alkenyl;        alkynyl; cycloalkyl; cycloalkenyl; cycloalkynyl; aryl;        arylalkyl; heterocyclic; heterocyclic-alkyl; acyloxyalkyl;        acyloxyalkenyl; acyloxyalkynyl; acyloxyaryl; acyloxyarylalkyl;        acyloxyarylalkenyl; acyloxyarylalkynyl; dialkylcarbonate;        alkylarylcarbonate; alkylalkenylcarbonate;        alkylalkynylcarbonate; alkenylarylcarbonate;        alkynyl-arylcarbonate; alkenylalkynylcarbonate;        dialkenylcarbonate; dialkynylcarbo-nate; wherein said alkyl,        alkenyl and alkynyl optionally contains one or more heteroatoms        in or at the end of the hydrocarbon chain, said heteroatoms        being independently selected from the group consisting of        oxygen, sulfur and nitrogen;    -   R³, R⁴, R⁵, R⁶, R⁷ and R⁸ are each independently selected from        the group consisting of hydrogen, azido, halogen (preferably        fluoro), cyano, alkyl, alkenyl, alkynyl, SR¹⁴ and OR¹⁴;    -   R¹⁴ is selected from hydrogen; alkyl; alkenyl; alkynyl;        cycloalkyl; cycloalkenyl; cycloalkynyl; aryl; heterocyclic;        arylalkyl; heterocyclic-alkyl; acyloxyalkyl; wherein said alkyl,        alkenyl and alkynyl optionally contain one or more heteroatoms        in or at the end of the hydrocarbon chain, said heteroatoms        being independently selected from the group consisting of        oxygen, sulfur and nitrogen;    -   R¹⁶, R¹⁷ and R¹⁸ are independently selected from the group        consisting of hydrogen; alkyl; alkenyl; alkynyl; cycloalkyl;        cycloalkenyl; cycloalkynyl; aryl; arylalkyl; heterocyclic;        heterocyclic-alkyl; acyloxyalkyl; wherein said alkyl, alkenyl        and alkynyl optionally contain one or more heteroatoms in or at        the end of the hydrocarbon chain, said heteroatoms being        independently selected from the group consisting of oxygen,        sulfur and nitrogen;    -   X⁴ and R¹, or X⁵ and R² may together form an amino-acid residue        or polypeptide wherein a carboxyl function of said amino-acid        residue being at a distance from the amidate nitrogen not        further than 5 atoms is esterified;    -   X⁴ and R¹ or X⁵ and R² may together form a group having the        formula —OC(R⁹)₂OC(O)Y(R⁰)_(a) wherein Y═N or O, a=1 when Y is O        and a=1 or 2 when Y is N;    -   R⁹ is selected from the group consisting of hydrogen, alkyl,        aryl, alkenyl, alkynyl, alkenylaryl, alkynylaryl or alkylaryl,        wherein each of said alkyl, alkenyl, alkynyl and aryl groups is        optionally substituted with one or more atoms or groups selected        from the group consisting of halo, cyano, azido, nitro and OR¹⁴;    -   R¹⁰ is selected from the group consisting of hydrogen, alkyl,        aryl, alkenyl, alkynyl, alkenylaryl, alkynylaryl and alkylaryl,        wherein each of said alkyl, alkenyl, alkynyl and aryl groups is        optionally substituted with one or more atoms or groups selected        from the group consisting of halo, cyano, azido, nitro, OR¹⁴ and        NR¹¹R¹²;    -   R¹¹ and R¹² are each independently selected from the group        consisting of hydrogen and alkyl;    -   n is an integer representing the number of methylene groups        between and P, each of said methylene groups being optionally        and independently substituted with one or two substituents        selected from the group consisting of halogen, hydroxyl,        sulhydryl and C₁₋₄alkyl, and n being selected from 1, 2, 3, 4, 5        and 6; and    -   m is 0 or 1,        including pharmaceutically acceptable salts, solvates, isomers        and prodrugs thereof.

More specific embodiments of the invention include sub-classes ofstereoisomers represented by any of the following formulae (III) to(XVIII):

wherein n, m, B, X¹, X², X³, X⁴, X⁵, R¹, R², R³, R⁴, R⁵, R⁶, R⁷, R⁸, R⁹,R¹⁰, R¹¹, R¹², R¹⁴, R¹⁶, R¹⁷ and R¹⁸ are defined as in formula (II),including pharmaceutically acceptable salts, solvates, isomers andprodrugs thereof.

In a specific embodiment, this invention relates to compoundsrepresented by any of the formulae (II) to (XVIII), wherein R⁴ ishydroxy.

In a preferred embodiment, this invention relates to compoundsrepresented by any of the formulae (II) to (XVIII), wherein at least oneof R⁷ and R⁸ is hydrogen, more preferably both R⁷ and R⁸ are hydrogen.

In its more general acceptance, the invention also relates to a secondclass of compounds including a heterocyclic nucleobase attached to afirst carbon atom of an optionally substituted five-membermono-unsaturated heterocyclic group selected from dihydrofuranyl anddihydrothienyl and further including a phosphonoalkoxy,thiophosphonoalkoxy, phosphonothioalkyl or thiophosphonothioalkyl groupattached to a second carbon atom of said five-member mono-unsaturatedheterocyclic group, said first carbon atom being adjacent to theheteroatom of said five-member mono-unsaturated heterocyclic group, andsaid second carbon atom being adjacent neither to the heteroatom nor tothe first carbon atom of said five-member mono-unsaturated heterocyclicgroup. This second class of compounds may be represented by the generalformula (XIX):

wherein:

-   -   X¹, X², X³, X⁴ and X⁵ are each each independently selected from        the group consisting of oxygen and sulfur,    -   B is a natural or non-natural heterocyclic nucleobase,    -   R¹ and R² are each independently selected from the group        consisting of hydrogen; (—PO₃R¹⁶)_(m)—PO₃R¹⁷R¹⁸; alkyl; alkenyl;        alkynyl; cycloalkyl; cycloalkenyl; cycloalkynyl; aryl;        arylalkyl; heterocyclic; heterocyclic-alkyl; acyloxyalkyl;        acyloxyalkenyl; acyloxyalkynyl; acyloxyaryl; acyloxyarylalkyl;        acyloxyarylalkenyl; acyloxyarylalkynyl; dialkylcarbonate;        alkylarylcarbonate; alkylalkenylcarbonate;        alkylalkynylcarbonate; alkenylarylcarbonate;        alkynyl-arylcarbonate; alkenylalkynylcarbonate;        dialkenylcarbonate; dialkynyl-carbonate; wherein said alkyl,        alkenyl and alkynyl optionally contain one or more heteroatoms        in or at the end of the hydrocarbon chain, said heteroatoms        being independently selected from the group consisting of        oxygen, sulfur and nitrogen;    -   R³, R⁴, R⁷ and R⁸ are each independently selected from the group        consisting of hydrogen, azido, halogen (preferably fluoro),        cyano, alkyl, alkenyl, alkynyl, SR¹⁴ and OR¹⁴;    -   R¹⁴ is selected from hydrogen; alkyl; alkenyl; alkynyl;        cycloalkyl; cycloalkenyl; cycloalkynyl; aryl; heterocyclic;        arylalkyl; heterocyclic-alkyl; acyloxyalkyl; wherein said alkyl,        alkenyl and alkynyl optionally contain one or more heteroatoms        in or at the end of the hydrocarbon chain, said heteroatoms        being independently selected from the group consisting of        oxygen, sulfur and nitrogen;    -   R¹⁶, R¹⁷ and R¹⁸ are independently selected from the group        consisting of hydrogen; alkyl; alkenyl; alkynyl; cycloalkyl;        cycloalkenyl; cycloalkynyl; aryl; arylalkyl; heterocyclic ring;        heterocyclic ring-alkyl; acyloxyalkyl; wherein said alkyl,        alkenyl and alkynyl optionally contain one or more heteroatoms        in or at the end of the hydrocarbon chain, said heteroatoms        being independently selected from the group consisting of        oxygen, sulfur and nitrogen;    -   X⁴ and R¹, or X⁵ and R² may together form an amino-acid residue        or polypeptide wherein a carboxyl function of said amino-acid        residue being at a distance from the amidate nitrogen not        further than 5 atoms is esterified;    -   X⁴ and R¹ or X⁵ and R² may together form a group having the        formula —OC(R⁹)₂OC(O)Y(R¹⁰)_(a) wherein Y═N or O, a=1 when Y is        O and a=1 or 2 when Y is N;    -   R⁹ is selected from the group consisting of hydrogen, alkyl,        aryl, alkenyl, alkynyl, alkenylaryl, alkynylaryl or alkylaryl,        wherein each of said alkyl, alkenyl, alkynyl and aryl groups is        optionally substituted with one or more atoms or groups selected        from the group consisting of halo, cyano, azido, nitro and OR¹⁴;    -   R¹⁰ is selected from the group consisting of hydrogen, alkyl,        aryl, alkenyl, alkynyl, alkenylaryl, alkynylaryl and alkylaryl,        wherein each of said alkyl, alkenyl, alkynyl and aryl groups is        optionally substituted with one or more atoms or groups selected        from the group consisting of halo, cyano, azido, nitro, OR¹⁴ and        NR¹¹R¹²;    -   R¹¹ and R¹² are each independently selected from the group        consisting of hydrogen and alkyl;    -   n is an integer representing the number of methylene groups        between and P, each of said methylene groups being optionally        and independently substituted with one or two substituents        selected from the group consisting of halogen, hydroxyl,        sulhydryl and C₁₋₄ alkyl, and n being selected from 1, 2, 3, 4,        5 and 6; and    -   m is 0 or 1,        including pharmaceutically acceptable salts, solvates, isomers        and prodrugs thereof.

More specific embodiments of the invention include sub-classes ofcompounds being stereoisomers represented by any of the followingformulae (XX) to (XXVI):

wherein n, m, B, X¹, X², X³, X⁴, X⁵, R¹, R², R³, R⁴, R⁷, R⁸, R⁹, R¹⁰,R¹¹, R¹², R¹⁴, R¹⁶, R¹⁷ and R¹⁸ are defined as in formula (XIX), andwherein the snake-like symbol stands for any stereochemical arrangementof the respective bond, including pharmaceutically acceptable salts,solvates, isomers and prodrugs thereof.

In a specific embodiment, this invention relates to compoundsrepresented by any of the formulae (XIX) to (XXVI), wherein R⁴ ishydroxy.

In a preferred embodiment, this invention relates to compoundsrepresented by any of the formulae (XIX) to (XXVI), wherein at least oneof R⁷ and R⁸ is hydrogen, more preferably wherein both R⁷ and R⁸ arehydrogen.

It should be understood that in the above embodiments of the invention,the novel compounds are as defined in any of the general formulae (I) to(XXVI), wherein:

-   -   each of the substituents B, X¹, X², X³, X⁴, X⁵, R¹, R², R³, R⁴,        R⁵, R⁶, R⁷, R⁸, R⁹, R¹⁰, R¹¹, R¹², R¹⁴, R¹⁶, R¹⁷ and R¹⁸ may        independently correspond to any of the definitions given above,        in particular with any of the preferred ranges or individual        meanings (such as illustrated above) of generic terms used for        substituting radicals such as, but not limited to, “alkyl”,        “cycloalkyl”, “alkenyl”, “alkynyl”, “aryl”, “heterocyclic”,        “halogen”, “cycloalkenyl”, “alkylaryl”, “arylalkyl”, “alkoxy”,        “cycloalkoxy”, “thioalkyl”, “thiocyclo-alkyl”, “amino-acid” and        the like,    -   each of the integers m and n may independently correspond to any        of the individual values given above.

In each of the formulae (I) to (XXVI), the alkylene chain between X² andthe phosphorus atom P is preferably a short chain, i.e. n is preferably1 or 2. This alkylene chain may also include one or more substituentssuch as halogen, hydroxyl, sulhydryl and methyl, for instance it may beany of —CYY′—, —CHY—, —CYY′—CY″Y′″— or —CHY—CY′Y″—, each of Y, Y′, Y″and Y″′ being preferably independently selected from the groupconsisting of fluoro, chloro, hydroxyl, sulhydryl and methyl.

It should be understood that R¹ and R² refers to the definitions ofphosphonate prodrugs such as described for example in U.S. Pat. No.6,225,460 and U.S. Pat. No. 5,977,089.

Specific embodiments of bases B suitable for inclusion into thecompounds of the present invention include, but are not limited to,hypoxanthine, guanine, adenine, cytosine, inosine, thymine, uracil,xanthine, 8-aza derivatives of 2-aminopurine, 2,6-diaminopurine,2-amino-6-chloropurine, hypoxanthine, inosine and xanthine;7-deaza-8-aza derivatives of adenine, guanine, 2-aminopurine,2,6-diaminopurine, 2-amino-6-chloropurine, hypoxanthine, inosine andxanthine; 1-deaza derivatives of 2-aminopurine, 2,6-diaminopurine,2-amino-6-chloropurine, hypoxanthine, inosine and xanthine; 7-deazaderivatives of 2-aminopurine, 2,6-diaminopurine, 2-amino-6-chloropurine,hypoxanthine, inosine and xanthine; 3-deaza derivatives of2-aminopurine, 2,6-diaminopurine, 2-amino-6-chloropurine, hypoxanthine,inosine and xanthine; 6-azacytosine; 5-fluorocytosine; 5-chlorocytosine;5-iodocytosine; 5-bromocytosine; 5-methylcytosine; 5-bromovinyluracil;5-fluorouracil; 5-chlorouracil; 5-iodouracil; 5-bromouracil;5-trifluoromethyluracil; 5-methoxymethyluracil; 5-ethynyluracil and5-propynyluracil. Preferably, B is a 9-purinyl residue selected fromguanyl, 3-deazaguanyl, 1-deazaguanyl, 8-azaguanyl, 7-deazaguanyl,adenyl, 3-deazaadenyl, 1-dezazadenyl, 8-azaadenyl, 7-deazaadenyl,2,6-diaminopurinyl, 2-aminopurinyl, 6-chloro-2-aminopurinyl and6-thio-2-aminopurinyl.

A particular embodiment of the present invention provides thephosphonate substituted nucleosides having any of the formulae (I) to(XXVI) wherein B is selected from adenine and thymine. Anotherparticular embodiment of the present invention provides novel3′-phosphonate substituted threose nucleosides, more particularly3′-phosphonalkoxy substituted threose nucleosides. In another particularembodiment of the present invention, the 3′-phosphonalkoxy substituentor the purine or pyrimidine bases coupled to the ring of the compoundsof the invention are in the R or S configuration.

The present invention also relates to certain novel intermediates thatare made and used during the course of manufacturing one or more of thephosphonate substituted nucleosides having any of the formulae (I) to(XXVI). Such novel intermediates may be represented by the followinggeneral formulae (XXVII) to (XXXVI):

wherein:

-   -   U is an acyl group,    -   V is a silyl group,    -   W is an alkyl group,    -   B^(p) is an optionally protected heterocyclic nucleobase,        wherein the protecting group may be acyl, silyl or benzyl ether,        and    -   Phos is an O-protected phosphonoalkoxy or thiophosphonoalkoxy        group or an S-protected phosphonothioalkyl or        thiophosphonothioalkyl group, wherein the protecting group is        one suitable for the protection of hydroxyl groups of a        phosphonic or thiophosphonic acid.

The present invention relates in a particular embodiment to novelcompounds and intermediates selected from the group consisting of:

-   1-(N⁶-benzoyladenin-9-yl)-2-O-benzoyl-3-O-(diisopropylphosphonomethyl)-L-threose    (11),-   1-(thymin-1-yl)-2-O-benzoyl-3-O-(diisopropylphosphonomethyl)-L-threose    (12),-   1-(uracil-1-yl)-2-O-benzoyl-3-O-(diisopropylphosphonomethyl)-L-threose    (13),-   1-(N⁴-acetylcytosin-1-yl)-2-O-benzoyl-3-O-(d iisopropyl    phosphonomethyl)-L-threose (14),-   1-(adenin-9-yl)-3-O-(diisopropylphosphonomethyl)-L-threose, also    named    (2R,3R,4S)—N⁹-[tetrahydro-3-hydroxy-4-(di-O-isopropylphosphonomethoxy)-furanyl]adenine    (15),-   1-(thymin-1-yl)-3-O-(diisopropylphosphonomethyl)-L-threose, also    named    (2R,3R,4S)—N¹-[tetrahydro-3-hydroxy-4-(di-O-isopropylphosphonomethoxy)-furanyl]thymine    (16),-   1-(uracil-1-yl)-3-O-(diisopropylphosphonomethyl)-L-threose, also    named    (2R,3R,4S)—N¹-[tetrahydro-3-hydroxy-4-(di-O-isopropylphosphonomethoxy)-furanyl]uracile    (17),-   1-(cytosin-1-yl)-3-O-(diisopropylphosphonomethyl)-L-threose, also    named    (2R,3R,4S)—N¹-[tetrahydro-3-hydroxy-4-(di-O-isopropylphosphonomethoxy)-furanyl]cytosine    (18),-   1-(adenin-9-yl)-2-deoxy-3-O-(diisopropylphosphonomethyl)-L-threose,    also named    (2R,4R)—N⁹-[tetrahydro-4-(di-O-isopropylphosphonomethoxy)-furanyl]adenine    (19),-   1-(thymin-1-yl)-2-deoxy-3-O-(diisopropylphosphonomethyl)-L-threose,    also named    (2R,4R)—N¹-[tetrahydro-4-(di-O-isopropylphosphonomethoxy)-furanyl]thymine    (20),-   1-(uracil-1-yl)-2-deoxy-3-O-(diisopropylphosphonomethyl)-L-threose,    also named    (2R,4R)—N′-[tetrahydro-4-(di-O-isopropylphosphonomethoxy)-furanyl]uracile    (21),-   1-(cytosin-1-yl)-2-deoxy-3-O-(diisopropylphosphonomethyl)-L-threose,    also named    (2R,4R)—N¹-[tetrahydro-4-(di-O-isopropylphosphonomethoxy)-furanyl]cytosine    (22),-   1-(adenin-9-yl)-3-O-(phosphonomethyl)-L-threose sodium salt, also    named    (2R,3R,4S)—N⁹-[tetrahydro-3-hydroxy-4-(phosphonomethoxy)-furanyl]adenine    sodium salt (3a),-   1-(thymin-1-yl)-3-O-(phosphonomethyl)-L-threose sodium salt, also    named    (2R,3R,4S)—N⁹-[tetrahydro-3-hydroxy-4-(phosphonomethoxy)-furanyl]thymine    sodium salt (3b),-   1-(uracil-1-yl)-3-O-(phosphonomethyl)-L-threose sodium salt, also    named    (2R,3R,4S)—N⁹-[tetrahydro-3-hydroxy-4-(phosphonomethoxy)-furanyl]uracile    sodium salt (3c),-   1-(cytosin-1-yl)-3-O-(phosphonomethyl)-L-threose sodium salt, also    named    (2R,3R,4S)—N⁹-[tetrahydro-3-hydroxy-4-(phosphonomethoxy)-furanyl]cytosine    sodium salt (3d),-   1-(adenin-1-yl)-2-deoxy-3-O-(phosphonomethyl)-L-threose sodium salt,    also named    (2R,4R)—N⁹-[tetrahydro-4-(phosphonomethoxy)-furanyl]adenine sodium    salt (3e),-   1-(thymin-1-yl)-2-deoxy-3-O-(phosphonomethyl)-L-threose sodium salt,    also named    (2R,4R)—N⁹-[tetrahydro-4-(phosphonomethoxy)-furanyl]thymine sodium    salt (3f),-   1-(uracil-1-yl)-2-deoxy-3-O-(phosphonomethyl)-L-threose sodium salt,    also named    (2R,4R)—N⁹-[tetrahydro-4-(phosphonomethoxy)-furanyl]uracile sodium    salt (3g),-   1-(cytidin-1-yl)-2-deoxy-3-O-(phosphonomethyl)-L-threose sodium    salt, also named    (2R,4R)—N⁹-[tetrahydro-4-(phosphonomethoxy)-furanyl]cytosine sodium    salt (3h),-   (3R,4S)-tetrahydro-4-hydroxy-3-O-tertbutyldimethylsilyl-furan-2-one,-   (3R,4S)-tetrahydro-4-O-benzoyl-3-O-tertbutyldimethylsilyl-furan-2-one,-   (2R/S,3R,4S)-tetrahydro-4-O-benzoyl-2-O-methyl-3-O-tertbutyldimethylsilyl-furan-2-one,-   (2S,3R,4S)-tetrahydro-2,3-di-O-tertbutyldimethylsilyl-4-hydroxy-furane,-   (2R,3R,4S)-tetrahydro-2,3-di-O-tertbutyldimethylsilyl-4-hydroxy-furane,-   (2S,3R,4S)-tetrahydro-2,3-di-O-tertbutyldimethylsilyl-4-(di-O-isopropylphos-phonomethoxy)-furane,-   (2R,3R,4S)-tetrahydro-2,3-di-O-tertbutyldimethylsilyl-4-(di-O-isopropylphos-phonomethoxy)-furane,-   (2S,3R,4S)-tetrahydro-2,3-di-O-benzoyl-4-(di-O-isopropylphosphonomethoxy)furane,-   (2R,3R,4S)-tetrahydro-2,3-di-O-benzoyl-4-(di-O-isopropylphosphonomethoxy)furane,-   (2R,3R,4S)—N⁶-benzoyl-N⁹-[Tetrahydro-3-O-benzoyl-4-(di-O-isopropylphos-phonomethoxy)-furanyl]adenine,-   (2R,3R,4S)—N¹-[tetrahydro-3-O-benzoyl-4-(di-O-isopropylphosphonomethoxy)-furanyl]thymine,-   (2R,3R,4S)—N¹-[tetrahydro-3-O-benzoyl-4-(di-O-isopropylphosphonomethoxy)-furanyl]uracile,    and-   (2R,3R,4S)—N⁶-acetyl-N′-[Tetrahydro-3-O-benzoyl-4-(di-O-isopropylphospho-nomethoxy)-furanyl]cytosine.

According to a second aspect, the invention relates to the use ofphosphonate substituted nucleosides of the formulae (I) to (XXXVI) asantiviral compounds, more particularly as compounds active against HIV.The invention also relates to the use of phosphonate substitutednucleosides of the formulae (I) to (XXXVI) for the manufacture of amedicine or as a pharmaceutically active ingredient, especially as avirus replication inhibitor, preferably a retrovirus replicationinhibitor, for instance for the manufacture of a medicament orpharmaceutical composition having antiviral activity for the preventionand/or treatment of viral, preferably retroviral, infections in humansand mammals. The present invention further relates to a method oftreatment of a viral infection, preferably a retroviral infection in amammal, including a human, comprising administering to the mammal inneed of such treatment a therapeutically effective amount of a compoundof any of formulae (I) to (XXXVI) as an active ingredient, preferably inadmixture with at least a pharmaceutically acceptable carrier.

The invention further relates to methods for the preparation ofcompounds of formulae (I) to (XXXVI). The process for preparing thephosphonoalkoxy substituted nucleosides of the present inventioncomprises the steps of selectively protecting the hydroxy functionspresent on the five-membered ring that can not react in the followingstep, reacting the remaining free hydroxy of the protected five-memberedring with protected phosphonylalkyl, followed by reaction with apyrimidine or purine base, deprotection of the five-membered ringprotecting groups and possible purine or pyrimidine base protectinggroups, if necessary a deoxygenation step of the hydroxy funstionspresent on the five-membered ring and finally a deprotection of thephosphonate protecting groups.

The invention also relates to pharmaceutical compositions comprising acompound of the invention according to any of the previous formulae (I)to (XXXVI) as an active ingredient in admixture with at least apharmaceutically acceptable carrier, the active ingredient being in aconcentration of at least about 0.1%, preferably at least 1%, morepreferably at least 3%, most preferably at least 5%, by weight of thecomposition. Preferably the active ingredient is in a concentration ofat most about 50%, more preferably at most 30%, most preferably at most20% by weight of the composition.

The invention further relates to a pharmaceutical compositioncomprising:

-   (a) one or more compounds having any of the general formulae (I) to    (XXXVI), and-   (b) one or more other anti-viral agents, preferably one or more    retroviral enzyme inhibitors    as biologically active agents, in admixture with at least a    pharmaceutically acceptable carrier, (a) and (b) preferably being in    respective proportions such as to provide a synergistic effect    against a viral infection (preferably a lentiviral infection and    more preferably a retroviral infection) in a mammal. This    composition for instance may be in the form of a combined    preparation for simultaneous or sequential use in viral, preferably    retroviral, infection therapy.

Within the framework of this embodiment of the invention, the retroviralenzyme inhibitors that may be used as therapeutically active ingredients(b) for co-administration include, among others, the following:

-   -   HIV-1 integrase inhibitors such as reviewed for instance in WO        02/051419,    -   reverse transcriptase inhibitors such as, but not limited to,        delavirdine, dideoxyadenosine, foscarnet sodium, stavudine,        suramin sodium, zalcitabine and the like,    -   nucleoside reverse transcriptase inhibitors such as, but not        limited to, for instance azidothymidine, zidovudine, lamivudine,        didanosine, abacavir, adefovir and the like,    -   nucleotide reverse transcriptase inhibitors such as, but not        limited to, for instance tenofovir,    -   non-nucleoside reverse transcriptase inhibitors such as, but not        limited to, nevirapine, efavirenz and the like,    -   HIV-1 protease inhibitors such as, but not limited to,        saquinavir, ritonavir, indinavir, nelfinavir, amprenavir,        fosamprenavir and the like, and    -   HIV fusion inhibitors such as enfuvirtide, and inhibitors of HIV        membrane fusion such as described in U.S. Pat. No. 6,818,710 and        U.S. Pat. No. 6,841,657.        Other suitable antiviral agents for inclusion into the above        antiviral compositions or combined preparations include for        instance acyclovir, cidofovir, cytarabine, edoxudine,        famciclovir, floxuridine, ganciclovir, idoxuridine, penciclovir,        sorivudine, trifluridine, valaciclovir, vidarabine, kethoxal,        methisazone, moroxydine, podophyllotoxin, ribavirine,        rimantadine, stallimycine, statolon, tromantadine and xenazoic        acid.

The invention also relates to compounds according to any of the generalformulae (I) to (XXXVI) being used for inhibiting the proliferation ofother viruses than HIV, preferably hepatitis B virus, hepatitis C virus,human papilloma virus or flaviviruses, in particular yellow fever virusor Dengue virus.

More generally, the invention relates to the compounds of formulae (I)to (XXXVI) being useful as agents having biological activity (preferablyantiviral or antitumoral activity) or as diagnostic agents. Any of theuses mentioned with respect to the present invention may be restrictedto a non-medical use, a non-therapeutic use, a non-diagnostic use, orexclusively an in vitro use, or a use related to cells remote from ananimal.

Another aspect of the invention relates to a pharmaceutical compositioncomprising a phosphonalkoxy-substituted orphosphonothioalkyl-substituted nucleoside of the invention according toany of formulae (I) to (XXXVI), more in particular having antiviralactivity, yet more in particular against HIV.

A further aspect of the invention provides for a method of treatment orprevention of a viral infection in a mammal, comprising administering tothe mammal in need of such treatment a therapeutically effective amountof a phosphonalkoxy-substituted or phosphonothioalkyl-substitutednucleoside according to any of formulae (I) to (XXXVI).

The compounds of the invention optionally are bound covalently to aninsoluble matrix and used for affinity chromatography (separations,depending on the nature of the groups of the compounds, for examplecompounds with aryl are useful in hydrophobic affinity separations.

The compounds of the invention are employed for the treatment orprophylaxis of viral infections, more particularly HIV infections. Whenusing one or more compounds according to any of the formulae (I) to(XXXVI) as defined herein:

-   -   the active ingredients of the compound(s) may be administered to        the mammal (including a human) to be treated by any means well        known in the art, i.e. orally, intranasally, subcutaneously,        intramuscularly, intradermally, intravenously, intra-arterially,        parenterally or by catheterization.    -   the therapeutically effective amount of the preparation of the        compound(s), especially for the treatment of viral infections in        humans and other mammals, preferably is a retroviral enzyme        inhibiting amount. More preferably, it is a retroviral        replication inhibiting amount or a retroviral enzyme inhibiting        amount of the compounds of formulae (I) to (XXXVI) as defined        herein. Depending upon the pathologic condition to be treated        and the patient's condition, the said effective amount may be        divided into several sub-units per day or may be administered at        more than one day intervals.

The present invention further relates to a method for preventing ortreating a viral infections in a subject or patient by administering tothe patient in need thereof a therapeutically effective amount ofphosphonate nucleosides of the present invention.

The therapeutically effective amount of the preparation of thecompound(s), especially for the treatment of viral infections in humansand other mammals, preferably is HIV protein/enzyme inhibiting amount.More preferably, it is a HIV replication inhibiting amount or a HIVenzyme inhibiting amount of the derivative(s) of the formulas as definedherein. Depending upon the pathologic condition to be treated and thepatient's condition, the effective amount may be divided into severalsub-units per day or may be administered at more than one day intervals.

As is conventional in the art, the evaluation of a synergistic effect ina drug combination may be made by analyzing the quantification of theinteractions between individual drugs, using the median effect principledescribed by Chou et al. in Adv. Enzyme Reg. (1984) 22:27. Briefly, thisprinciple states that interactions (synergism, additivity, antagonism)between two drugs can be quantified using the combination index(hereinafter referred as CI) defined by the following equation:

${CI}_{x} = {\frac{{ED}_{x}^{1c}}{{ED}_{x}^{1a}} + \frac{{ED}_{x}^{2c}}{{ED}_{x}^{2a}}}$

wherein ED, is the dose of the first or respectively second drug usedalone (1a, 2a), or in combination with the second or respectively firstdrug (1c, 2c), which is needed to produce a given effect. The said firstand second drug have synergistic or additive or antagonistic effectsdepending upon CI<1, CI=1, or CI>1, respectively.

Synergistic activity of the pharmaceutical compositions or combinedpreparations of this invention against viral infection may also bereadily determined by means of one or more tests such as, but notlimited to, the isobologram method, as previously described by Elion etal. in J. Biol. Chem. (1954) 208:477-488 and by Baba et al. inAntimicrob. Agents Chemother. (1984) 25:515-517, using EC₅₀ forcalculating the fractional inhibitory concentration (hereinafterreferred as FIC). When the minimum FIC index corresponding to the FIC ofcombined compounds (e.g., FIC_(x)+FIC_(y)) is equal to 1.0, thecombination is said to be additive; when it is between 1.0 and 0.5, thecombination is defined as subsynergistic, and when it is lower than 0.5,the combination is defined as synergistic. When the minimum FIC index isbetween 1.0 and 2.0, the combination is defined as subantagonistic and,when it is higher than 2.0, the combination is defined as antagonistic.

This principle may be applied to a combination of different antiviraldrugs of the invention or to a combination of the antiviral drugs of theinvention with other drugs that exhibit anti-HIV activity.

The invention thus relates to a pharmaceutical composition or combinedpreparation having synergistic effects against a viral infection andcontaining:

-   (a) a combination of two or more of the phosphonate nucleosides of    the present invention, and-   (b) optionally one or more pharmaceutical excipients or    pharmaceutically acceptable carriers,    for simultaneous, separate or sequential use in the treatment or    prevention of a viral infection, or-   (c) one or more anti-viral agents, and-   (d) at least one of the phosphonate nucleosides of the present    invention, and-   (e) optionally one or more pharmaceutical excipients or    pharmaceutically acceptable carriers,    for simultaneous, separate or sequential use in the treatment or    prevention of a viral infection.

Suitable anti-viral agents for inclusion into the synergistic antiviralcompositions or combined preparations of this invention includepractically all known anti-HIV compounds known at this moment such asnucleoside and non-nucleoside reverse transcriptase inhibitors, proteaseinhibitors and integrase inhibitors.

The pharmaceutical composition or combined preparation with synergisticactivity against viral infection according to this invention may containthe phosphonate nucleosides of the present invention, compoundsaccording to any of the formulae (I) to (XXXVI), over a broad contentrange depending on the contemplated use and the expected effect of thepreparation.

According to a particular embodiment of the invention, the compounds ofthe invention may be employed in combination with other therapeuticagents for the treatment or prophylaxis of HIV infections. The inventiontherefore relates to the use of a composition comprising:

-   (a) one or more compounds represented by any of formulae (I) to    (XXXVI), and-   (b) one or more HIV/protein-enzyme inhibitors as biologically active    agents in respective proportions such as to provide a synergistic    effect against a viral infection, particularly a HIV infection in a    mammal, for instance in the form of a combined preparation for    simultaneous, separate or sequential use in viral infection therapy,    such as HIV.    When using a combined preparation of (a) and (b):    -   the active ingredients (a) and (b) may be administered to the        mammal (including a human) to be treated by any means well known        in the art, i.e. orally, intranasally, subcutaneously,        intramuscularly, intradermally, intra-venously,        intra-arterially, parenterally or by catheterization.    -   the therapeutically effective amount of the combined preparation        of (a) and (b), especially for the treatment of viral infections        in humans and other mammals, particularly is a HIV enzyme        inhibiting amount. More particularly, it is a HIV replication        inhibiting amount of derivative (a) and a HIV enzyme inhibiting        amount of inhibitor (b). Still more particularly when the said        HIV enzyme inhibitor (b) is a reverse transcriptase inhibitor,        its effective amount is a reverse transcriptase inhibiting        amount. When the said HIV enzyme inhibitor (b) is a protease        inhibitor, its effective amount is a protease inhibiting amount.    -   ingredients (a) and (b) may be administered simultaneously but        it is also beneficial to administer them separately or        sequentially, for instance within a relatively short period of        time (e.g. within about 24 hours) in order to achieve their        functional fusion in the body to be treated.

The invention also relates to the compounds of the invention, compoundsaccording to any of the formulae (I) to (XXXVI) which can be screenedfor inhibition of the proliferation of other viruses than HIV,particularly for the inhibition of other retroviruses and lentivirusesand also for the inhibition of flaviviruses or picornaviruses such asBVDV, HCV, HBV or Coxsackie virus, with in particular yellow fevervirus, Dengue virus, hepatitis B virus, hepatitis G virus, ClassicalSwine Fever virus or the Border Disease Virus. Als other viruses may beinhibited such as HSV, CMV and Sars-virus.

The present invention further provides veterinary compositionscomprising at least one active ingredient as above defined together witha veterinary carrier therefore. Veterinary carriers are materials usefulfor the purpose of administering the composition and may be solid,liquid or gaseous materials which are otherwise inert or acceptable inthe veterinary art and are compatible with the active ingredient. Theseveterinary compositions may be administered orally, parenterally or byany other desired route.

More generally, the invention relates to the compounds according to anyof the formulae (I) to (XXXVI) being useful as agents having biologicalactivity (particularly antiviral activity) or as diagnostic agents. Anyof the uses mentioned with respect to the present invention may berestricted to a non-medical use, a non-therapeutic use, a non-diagnosticuse, or exclusively an in vitro use, or a use related to cells remotefrom an animal.

Those of skill in the art will also recognize that the compounds of theinvention may exist in many different protonation states, depending on,among other things, the pH of their environment. While the structuralformulae provided herein depict the compounds in only one of severalpossible protonation states, it will be understood that these structuresare illustrative only, and that the invention is not limited to anyparticular protonation state, any and all protonated forms of thecompounds are intended to fall within the scope of the invention.

The term “pharmaceutically acceptable salts” as used herein means thetherapeutically active non-toxic salt forms which the compoundsaccording to the formulas of the application like (I), (II), (III) areable to form. Therefore, the compounds of this invention optionallycomprise salts of the compounds herein, especially pharmaceuticallyacceptable non-toxic salts containing, for example, Na⁺, Li⁺, K⁺, Ca²⁺and Mg²⁺. Such salts may include those derived by combination ofappropriate cations such as alkali and alkaline earth metal ions orammonium and quaternary amino ions with an acid anion moiety, typicallya carboxylic acid. The compounds of the invention may bear multiplepositive or negative charges. The net charge of the compounds of theinvention may be either positive or negative. Any associated counterions are typically dictated by the synthesis and/or isolation methods bywhich the compounds are obtained. Typical counter ions include, but arenot limited to ammonium, sodium, potassium, lithium, halides, acetate,trifluoroacetate, etc., and mixtures thereof. It will be understood thatthe identity of any associated counter ion is not a critical feature ofthe invention, and that the invention encompasses the compounds inassociation with any type of counter ion. Moreover, as the compounds canexist in a variety of different forms, the invention is intended toencompass not only forms of the compounds that are in association withcounter ions (e.g., dry salts), but also forms that are not inassociation with counter ions (e.g., aqueous or organic solutions).Metal salts typically are prepared by reacting the metal hydroxide witha compound of this invention. Examples of metal salts which are preparedin this way are salts containing Li⁺, Na⁺, and K⁺. A less soluble metalsalt can be precipitated from the solution of a more soluble salt byaddition of the suitable metal compound. In addition, salts may beformed from acid addition of certain organic and inorganic acids tobasic centers, typically amines, or to acidic groups. Examples of suchappropriate acids include, for instance, inorganic acids such ashydrohalic acids, e.g. hydrochloric or hydrobromic acid, sulfuric acid,nitric acid, phosphoric acid and the like; or organic acids such as, forexample, acetic, propanoic, hydroxyacetic, 2-hydroxypropanoic,2-oxopropanoic, lactic, pyruvic, oxalic (i.e. ethanedioic), malonic,succinic (i.e. butanedioic acid), maleic, fumaric, malic, tartaric,citric, methanesulfonic, ethanesulfonic, benzenesulfonic,p-toluenesulfonic, cyclohexanesulfamic, salicylic (i.e.2-hydroxybenzoic), p-aminosalicylic and the like. Furthermore, this termalso includes the solvates which the compounds according to the formulasof the application like (I), (II), (III) as well as their salts are ableto form, such as for example hydrates, alcoholates and the like.Finally, it is to be understood that the compositions herein comprisecompounds of the invention in their unionized, as well as zwitterionicform, and combinations with stoichiometric amounts of water as inhydrates.

Also included within the scope of this invention are the salts of theparental compounds with one or more amino acids, especially thenaturally-occurring amino acids found as protein components. The aminoacid typically is one bearing a side chain with a basic or acidic group,e.g., lysine, arginine or glutamic acid, or a neutral group such asglycine, serine, threonine, alanine, isoleucine, or leucine.

The compounds of the invention also include physiologically acceptablesalts thereof. Examples of physiologically acceptable salts of thecompounds of the invention include salts derived from an appropriatebase, such as an alkali metal (for example, sodium), an alkaline earth(for example, magnesium), ammonium and NX₄ ⁺ (wherein X is alkyl).Physiologically acceptable salts of an hydrogen atom or an amino groupinclude salts of organic carboxylic acids such as acetic, benzoic,lactic, fumaric, tartaric, maleic, malonic, malic, isethionic,lactobionic and succinic acids; organic sulfonic acids, such asmethanesulfonic, ethanesulfonic, benzenesulfonic and p-toluenesulfonicacids; and inorganic acids, such as hydrochloric, sulfuric, phosphoricand sulfamic acids. Physiologically acceptable salts of a compoundcontaining a hydroxy group include the anion of said compound incombination with a suitable cation such as Na⁺ and NX₄ ⁺ (wherein Xtypically is independently selected from H or an alkyl group). However,salts of acids or bases which are not physiologically acceptable mayalso find use, for example, in the preparation or purification of aphysiologically acceptable compound. All salts, whether or not derivedform a physiologically acceptable acid or base, are within the scope ofthe present invention.

The term “isomers” as used herein means all possible isomeric forms,including tautomeric and sterochemical forms, which the compoundsaccording to formulae (I) to (XXXVI) may possess, but not includingposition isomers. Typically, the structures shown herein exemplify onlyone tautomeric or resonance form of the compounds, but the correspondingalternative configurations are contemplated as well. Unless otherwisestated, the chemical designation of compounds denotes the mixture of allpossible stereochemically isomeric forms, said mixtures containing alldiastereomers and enantiorners (since the compounds according to theabove formulae have at least one chiral center) of the basic molecularstructure, as wel as the stereochemically pure or enriched compounds.More particularly, stereogenic centers may have either the R- orS-configuration, and multiple bonds may have either cis- ortrans-configuration.

Pure isomeric forms of the said compounds are defined as isomerssubstantially free of other enantiomeric or diastereomeric forms of thesame basic molecular structure. In particular, the term“stereoisomerically pure” or “chirally pure” relates to compounds havinga stereoisomeric excess of at least about 80% (i.e. at least 90% of oneisomer and at most 10% of the other possible isomers), preferably atleast 90%, more preferably at least 94% and most preferably at least97%. The terms “enantiomerically pure” and “diastereo-merically pure”should be understood in a similar way, having regard to the enantiomericexcess, respectively the diastereomeric excess, of the mixture inquestion.

Separation of stereoisomers is accomplished by standard methods known tothose in the art. One enantiomer of a compound of the invention can beseparated substantially free of its opposing enantiomer by a method suchas formation of diastereomers using optically active resolving agents(“Stereochemistry of Carbon Compounds” (1962) by E. L. Eliel, McGrawHill; Lochmuller, C. H., (1975) J. Chromatogr., 113:(3) 283-302).Separation of isomers in a mixture can be accomplished by any suitablemethod, including: (1) formation of ionic, diastereomeric salts withchiral compounds and separation by fractional, crystallization or othermethods, (2) formation of diastereomeric compounds with chiralderivatizing reagents, separation of the diastereomers, and conversionto the pure enantiomers, or (3) enantiomers can be separated directlyunder chiral conditions. Under method (1), diastereomeric salts can beformed by reaction of enantiomerically pure chiral bases such asbrucine, quinine, ephedrine, strychnine, a-methyl-b-phenylethylamine(amphetamine), and the like with asymmetric compounds bearing acidicfunctionality, such as carboxylic acid and sulfonic acid. Thediastereomeric salts may be induced to separate by fractionalcrystallization or ionic chromatography. For separation of the opticalisomers of amino compounds, addition of chiral carboxylic or sulfonicacids, such as camphorsulfonic acid, tartaric acid, mandelic acid, orlactic acid can result in formation of the diastereomeric salts.Alternatively, by method (2), the substrate to be resolved may bereacted with one enantiomer of a chiral compound to form adiastereomeric pair (Eliel, E. and Wilen, S. (1994) Stereochemistry ofOrganic Compounds, John Wiley & Sons, Inc., p. 322). Diastereomericcompounds can be formed by reacting asymmetric compounds withenantiomerically pure chiral derivatizing reagents, such as menthylderivatives, followed by separation of the diastereomers and hydrolysisto yield the free, enantiomerically enriched compounds of the invention.A method of determining optical purity involves making chiral esters,such as a menthyl ester or Mosher ester,a-methoxy-a-(trifluoromethyl)phenyl acetate (Jacob III. (1982) J. Org.Chem. 47:4165), of the racemic mixture, and analyzing the NMR spectrumfor the presence of the two atropisomeric diastereomers. Stablediastereomers can be separated and isolated by normal- and reverse-phasechromatography following methods for separation of atropisomericnaphthyl-isoquinolines (e.g. see WO96/15111). Under method (3), aracemic mixture of two asymmetric enantiomers is separated bychromatography using a chiral stationary phase. Suitable chiralstationary phases are, for example, polysaccharides, in particularcellulose or amylose derivatives. Commercially available polysaccharidebased chiral stationary phases are ChiralCel™ CA, OA, OB5, OC5, OD, OF,OG, OJ and OK, and Chiralpak™ AD, AS, OP(+) and OT(+). Appropriateeluents or mobile phases for use in combination with said polysaccharidechiral stationary phases are hexane and the like, modified with analcohol such as ethanol, isopropanol and the like. (“Chiral LiquidChromatography” (1989) W. J. Lough, Ed. Chapman and Hall, New York;Okamoto, (1990) “Optical resolution of dihydropyridine enantiomers byHigh-performance liquid chromatography using phenylcarbamates ofpolysaccharides as a chiral stationary phase”, J. of Chromatogr.513:375-378).

The terms cis and trans are used herein in accordance with ChemicalAbstracts nomenclature and include reference to the position of thesubstituents on a ring moiety. The absolute stereochemical configurationof the compounds according to the above formulae (I) to (XXXVI) mayeasily be determined by those skilled in the art while using well-knownmethods such as, for example, X-ray diffraction or NMR.

The compounds of the invention may be formulated with conventionalcarriers and excipients, which will be selected in accord with ordinarypractice. Tablets will contain excipients, glidants, fillers, bindersand the like. Aqueous formulations are prepared in sterile form, andwhen intended for delivery by other than oral administration generallywill be isotonic. Formulations optionally contain excipients such asthose set forth in the “Handbook of Pharmaceutical Excipients” (1986)and include ascorbic acid and other antioxidants, chelating agents suchas EDTA, carbohydrates such as dextrin, hydroxyalkylcellulose,hydroxyalkylmethylcellulose, stearic acid and the like.

The pharmaceutical compositions of this invention can suitably beprepared and used in the form of concentrates, emulsions, solutions,granulates, dusts, sprays, aerosols, suspensions, ointments, creams,tablets, pellets or powders.

Suitable pharmaceutical carriers for use in the said pharmaceuticalcompositions and their formulation are well known to those skilled inthe art, and there is no particular restriction to their selectionwithin the present invention. They may also include additives such aswetting agents, dispersing agents, stickers, adhesives, emulsifyingagents, solvents, coatings, antibacterial and antifungal agents (forexample phenol, sorbic acid, chlorobutanol), isotonic agents (such assugars or sodium chloride) and the like, provided the same areconsistent with pharmaceutical practice, i.e. carriers and additiveswhich do not create permanent damage to mammals. The pharmaceuticalcompositions of the present invention may be prepared in any knownmanner, for instance by homogeneously mixing, coating and/or grindingthe active ingredients, in a one-step or multi-steps procedure, with theselected carrier material and, where appropriate, the other additivessuch as surface-active agents may also be prepared by inicronisation,for instance in view to obtain them in the form of microspheres usuallyhaving a diameter of about 1 to 10 gm, namely for the manufacture ofmicrocapsules for controlled or sustained release of the activeingredients.

Suitable surface-active agents, also known as emulgent or emulsifier, tobe used in the pharmaceutical compositions of the present invention arenon-ionic, cationic and/or anionic materials having good emulsifying,dispersing and/or wetting properties. Suitable anionic surfactantsinclude both water-soluble soaps and water-soluble syntheticsurface-active agents. Suitable soaps are alkaline or alkaline-earthmetal salts, unsubstituted or substituted ammonium salts of higher fattyacids (C₁₀-C₂₂), e.g. the sodium or potassium salts of oleic or stearicacid, or of natural fatty acid mixtures obtainable form coconut oil ortallow oil. Synthetic surfactants include sodium or calcium salts ofpolyacrylic acids; fatty sulphonates and sulphates; sulphonatedbenzimidazole derivatives and alkylarylsulphonates. Fatty sulphonates orsulphates are usually in the form of alkaline or alkaline-earth metalsalts, unsubstituted ammonium salts or ammonium salts substituted withan alkyl or acyl radical having from 8 to 22 carbon atoms, e.g. thesodium or calcium salt of lignosulphonic acid or dodecylsulphonic acidor a mixture of fatty alcohol sulphates obtained from natural fattyacids, alkaline or alkaline-earth metal salts of sulphuric or sulphonicacid esters (such as sodium lauryl sulphate) and sulphonic acids offatty alcohol/ethylene oxide adducts. Suitable sulphonated benzimidazolederivatives preferably contain 8 to 22 carbon atoms. Examples ofalkylarylsulphonates are the sodium, calcium or alcanolamine salts ofdodecylbenzene sulphonic acid or dibutyl-naphtalenesulphonic acid or anaphtalene-sulphonic acid/formaldehyde condensation product. Alsosuitable are the corresponding phosphates, e.g. salts of phosphoric acidester and an adduct of p-nonylphenol with ethylene and/or propyleneoxide, or phospholipids. Suitable phospholipids for this purpose are thenatural (originating from animal or plant cells) or syntheticphospholipids of the cephalin or lecithin type such as e.g.phosphatidylethanolamine, phosphatidylserine, phosphatidylglycerine,lysolecithin, cardiolipin, dioctanylphosphatidyl-choline,dipalmitoylphoshatidyl-choline and their mixtures.

Suitable non-ionic surfactants include polyethoxylated andpolypropoxylated derivatives of alkylphenols, fatty alcohols, fattyacids, aliphatic amines or amides containing at least 12 carbon atoms inthe molecule, alkylarenesulphonates and dialkylsulphosuccinates, such aspolyglycol ether derivatives of aliphatic and cycloaliphatic alcohols,saturated and unsaturated fatty acids and alkylphenols, said derivativespreferably containing 3 to 10 glycol ether groups and 8 to 20 carbonatoms in the (aliphatic) hydrocarbon moiety and 6 to 18 carbon atoms inthe alkyl moiety of the alkylphenol. Further suitable non-ionicsurfactants are water-soluble adducts of polyethylene oxide withpoylypropylene glycol, ethylenediaminopolypropylene glycol containing 1to 10 carbon atoms in the alkyl chain, which adducts contain 20 to 250ethyleneglycol ether groups and/or 10 to 100 propyleneglycol ethergroups. Such compounds usually contain from 1 to 5 ethyleneglycol unitsper propyleneglycol unit. Representative examples of non-ionicsurfactants are nonylphenol-polyethoxyethanol, castor oil polyglycolicethers, polypropylene/polyethylene oxide adducts,tributylphenoxy-polyethoxyethanol, polyethyleneglycol andoctylphenoxypolyethoxyethanol. Fatty acid esters of polyethylenesorbitan (such as polyoxyethylene sorbitan trioleate), glycerol,sorbitan, sucrose and pentaerythritol are also suitable non-ionic surfactants.

Suitable cationic surfactants include quaternary ammonium salts,particularly halides, having 4 hydrocarbon radicals optionallysubstituted with halo, phenyl, substituted phenyl or hydroxy; forinstance quaternary ammonium salts containing as N-substituent at leastone C8C22 alkyl radical (e.g. cetyl, lauryl, palmityl, myristyl, oleyland the like) and, as further substituents, unsubstituted or halogenatedlower alkyl, benzyl and/or hydroxy-lower alkyl radicals.

A more detailed description of surface-active agents suitable for thispurpose may be found for instance in “McCutcheon's Detergents andEmulsifiers Annual” (MC Publishing Crop., Ridgewood, N.J., 1981),“Tensid-Taschenbucw′, 2 d ed. (Hanser Verlag, Vienna, 1981) and“Encyclopaedia of Surfactants, (Chemical Publishing Co., New York,1981).

Compounds of the invention and their physiologically acceptable salts(hereafter collectively referred to as the active ingredients) may beadministered by any route appropriate to the condition to be treated,suitable routes including oral, rectal, nasal, topical (includingocular, buccal and sublingual), vaginal and parenteral (includingsubcutaneous, intramuscular, intravenous, intradermal, intrathecal andepidural). The preferred route of administration may vary with forexample the condition of the recipient.

While it is possible for the active ingredients to be administered aloneit is preferable to present them as pharmaceutical formulations. Theformulations, both for veterinary and for human use, of the presentinvention comprise at least one active ingredient, as above described,together with one or more pharmaceutically acceptable carriers thereforeand optionally other therapeutic ingredients. The carrier(s) optimallyare “acceptable” in the sense of being compatible with the otheringredients of the formulation and not deleterious to the recipientthereof. The formulations include those suitable for oral, rectal,nasal, topical (including buccal and sublingual), vaginal or parenteral(including subcutaneous, intramuscular, intravenous, intradermal,intrathecal and epidural) administration. The formulations mayconveniently be presented in unit dosage form and may be prepared by anyof the methods well known in the art of pharmacy. Such methods includethe step of bringing into association the active ingredient with thecarrier which constitutes one or more accessory ingredients. In generalthe formulations are prepared by uniformly and intimately bringing intoassociation the active ingredient with liquid carriers or finely dividedsolid carriers or both, and then, if necessary, shaping the product.

Formulations of the present invention suitable for oral administrationmay be presented as discrete units such as capsules, cachets or tabletseach containing a predetermined amount of the active ingredient; as apowder or granules; as solution or a suspension in an aqueous liquid ora non-aqueous liquid; or as an oil-in-water liquid emulsion or awater-in-oil liquid emulsion. The active ingredient may also bepresented as a bolus, electuary or paste.

A tablet may be made by compression or molding, optionally with one ormore accessory ingredients. Compressed tablets may be prepared bycompressing in a suitable machine the active ingredient in afree-flowing form such as a powder or granules, optionally mixed with abinder, lubricant, inert diluent, preservative, surface active ordispersing agent. Molded tablets may be made by molding in a suitablemachine a mixture of the powdered compound moistened with an inertliquid diluent. The tablets may optionally be coated or scored and maybe formulated so as to provide slow or controlled release of the activeingredient therein. For infections of the eye or other external tissuese.g. mouth and skin, the formulations are optionally applied as atopical ointment or cream containing the active ingredient(s). Whenformulated in an ointment, the active ingredients may be employed witheither a paraffinic or a water-miscible ointment base. Alternatively,the active ingredients may be formulated in a cream with an oil-in-watercream base. If desired, the aqueous phase of the cream base may include,for example, at least 30% w/w of a polyhydric alcohol, i.e. an alcoholhaving two or more hydroxyl groups such as propylene glycol, butane1,3-diol, mannitol, sorbitol, glycerol and polyethylene glycol(including PEG400) and mixtures thereof. The topical formulations maydesirably include a compound which enhances absorption or penetration ofthe active ingredient through the skin or other affected areas. Examplesof such dermal penetration enhancers include dimethylsulfoxide andrelated analogs.

The oily phase of the emulsions of this invention may be constitutedfrom known ingredients in a known manner. While the phase may comprisemerely an emulsifier (otherwise known as an emulgent), it desirablycomprises a mixture of at least one emulsifier with a fat or an oil orwith both a fat and an oil. Optionally, a hydrophilic emulsifier isincluded together with a lipophilic emulsifier which acts as astabilizer. It is also preferred to include both an oil and a fat.Together, the emulsifier(s) with or without stabilizer(s) make up theso-called emulsifying wax, and the wax together with the oil and fatmake up the so-called emulsifying ointment base which forms the oilydispersed phase of the cream formulations. The choice of suitable oilsor fats for the formulation is based on achieving the desired cosmeticproperties, since the solubility of the active compound in most oilslikely to be used in pharmaceutical emulsion formulations is very low.Thus the cream should optionally be a non-greasy, non-staining andwashable product with suitable consistency to avoid leakage from tubesor other containers. Straight or branched chain, mono- or dibasic alkylesters such as di-isoadipate, isocetyl stearate, propylene glycoldiester of coconut fatty acids, isopropyl myristate, decyl oleate,isopropyl palmitate, butyl stearate, 2-ethylhexyl palmitate or a blendof branched chain esters known as Crodamol CAP may be used, the lastthree being preferred esters. These may be used alone or in combinationdepending on the properties required. Alternatively, high melting pointlipids such as white soft paraffin and/or liquid paraffin or othermineral oils can be used.

Formulations suitable for topical administration to the eye also includeeye drops wherein the active ingredient is dissolved or suspended in asuitable carrier, especially an aqueous solvent for the activeingredient. Formulations suitable for topical administration in themouth include lozenges comprising the active ingredient in a flavoredbasis, usually sucrose and acacia or tragacanth; pastilles comprisingthe active ingredient in an inert basis such as gelatin and glycerin, orsucrose and acacia; and mouthwashes comprising the active ingredient ina suitable liquid carrier.

Formulations for rectal administration may be presented as a suppositorywith a suitable base comprising for example cocoa butter or asalicylate. Formulations suitable for nasal administration wherein thecarrier is a solid include a coarse powder having a particle size forexample in the range 20 to 500 microns (including particle sizes in arange between 20 and 500 microns in increments of 5 microns such as 30microns, 35 microns, etc), which is administered in the manner in whichsnuff is taken, i.e. by rapid inhalation through the nasal passage froma container of the powder held close up to the nose. Suitableformulations wherein the carrier is a liquid, for administration as forexample a nasal spray or as nasal drops, include aqueous or oilysolutions of the active ingredient. Formulations suitable for aerosoladministration may be prepared according to conventional methods and maybe delivered with other therapeutic agents.

Formulations suitable for vaginal administration may be presented aspessaries, tampons, creams, gels, pastes, foams or spray formulationscontaining in addition to the active ingredient such carriers as areknown in the art to be appropriate.

Formulations suitable for parenteral administration include aqueous andnon-aqueous sterile injection solutions which may contain anti-oxidants,buffers, bacteriostats and solutes which render the formulation isotonicwith the blood of the intended recipient; and aqueous and non-aqueoussterile suspensions which may include suspending agents and thickeningagents. The formulations may be presented in unit-dose or multi-dosecontainers, for example sealed ampoules and vials, and may be stored ina freeze-dried (lyophilized) condition requiring only the addition ofthe sterile liquid carrier, for example water for injections,immediately prior to use. Extemporaneous injection solutions andsuspensions may be prepared from sterile powders, granules and tabletsof the kind previously described.

Preferred unit dosage formulations are those containing a daily dose orunit daily sub-dose, as herein above recited, or an appropriate fractionthereof, of an active ingredient.

It should be understood that in addition to the ingredients particularlymentioned above the formulations of this invention may include otheragents conventional in the art having regard to the type of formulationin question, for example those suitable for oral administration mayinclude flavoring agents.

Compounds of the invention can be used to provide controlled releasepharmaceutical formulations containing as active ingredient one or morecompounds of the invention (“controlled release formulations”) in whichthe release of the active ingredient can be controlled and regulated toallow less frequency dosing or to improve the pharmacokinetic ortoxicity profile of a given invention compound. Controlled releaseformulations adapted for oral administration in which discrete unitscomprising one or more compounds of the invention can be preparedaccording to conventional methods.

Additional ingredients may be included in order to control the durationof action of the active ingredient in the composition. Control releasecompositions may thus be achieved by selecting appropriate polymercarriers such as for example polyesters, polyamino acids, polyvinylpyrrolidone, ethylene-vinyl acetate copolymers, methylcellulose,carboxymethylcellulose, protamine sulfate and the like. The rate of drugrelease and duration of action may also be controlled by incorporatingthe active ingredient into particles, e.g. microcapsules, of a polymericsubstance such as hydrogels, polylactic acid, hydroxymethyl-cellulose,polymethyl methacrylate and the other above-described polymers. Suchmethods include colloid drug delivery systems like liposomes,microspheres, microemulsions, nanoparticles, nanocapsules and so on.Depending on the route of administration, the pharmaceutical compositionmay require protective coatings. Pharmaceutical forms suitable forinjectionable use include sterile aqueous solutions or dispersions andsterile powders for the extemporaneous preparation thereof. Typicalcarriers for this purpose therefore include biocompatible aqueousbuffers, ethanol, glycerol, propylene glycol, polyethylene glycol andthe like and mixtures thereof.

In view of the fact that, when several active ingredients are used incombination, they do not necessarily bring out their joint therapeuticeffect directly at the same time in the mammal to be treated, thecorresponding composition may also be in the form of a medical kit orpackage containing the two ingredients in separate but adjacentrepositories or compartments. In the latter context, each activeingredient may therefore be formulated in a way suitable for anadministration route different from that of the other ingredient, e.g.one of them may be in the form of an oral or parenteral formulationwhereas the other is in the form of an ampoule for intravenous injectionor an aerosol.

The present invention also provides synthetic methods and processes formaking compounds according to the general formulae (I) to (XXVI), asdetailed herein after. The processes described further are only meant asexamples and by no means are meant to limit the scope of the presentinvention. For a better understanding of the following description,reference is made to FIGS. 1 to 15.

The synthetic schemes in FIGS. 1 to 15 illustrate syntheses of the3′-O-phosphonate-tetrose and 3′-S-phosphonate-tetrose nucleosidederivatives of five naturally-occurring nucleobases (adenine, thymine,uracil, cytosine, guanine) starting from commercially available lactonecompounds, but these syntheses can be adapted to any heterocyclicnucleobase without inventive effort. Each figure will now be describedin details.

FIGS. 1A and 1B

The synthetic scheme as shown in FIGS. 1A and 1B comprises 11 steps forthe synthesis of the 3′-O-phosphonate and3′-O-phosphonate,2′-deoxy-tetrose nucleoside derivatives of 4naturally-occurring nucleobases (adenine, thymine, uracil, cytosine)starting from (R,S)-2,3-dihydroxy-dihydro-furan-1-one (4).

In the first step (a), the 2′-hydroxy group is selectively protected.The hydroxyl group in position 2 is selectively protected, preferably bysilylation, more specifically with a tert-butyl dimethylsilyl(hereinafter referred to as TBDMS) group using TBDMS-chloride(hereinafter referred to as TBDMSCI) in the presence of a reactant,preferably imidazole, in an organic solvent, for example acetonitrile(hereinafter referred to as ACN). Protection of the hydroxy group onthis position does not affect the stereochemical orientation at thecarbon atom that same position. Preferably, silyl-protection is carriedout starting at 0° C. up to room temperature.

In the second step of the synthesis, the free hydroxyl group on position3 is then independently protected, preferably by a base-labileprotecting group for example by acylation, preferably by benzoylation.The benzoyl group is introduced using benzoylchloride under basicconditions in an organic solvent, for example in pyridine.Derivatisation of the hydroxygroup on this position does not affect thestereochemical orientation at the carbon atom that same position.Preferably, acylation (here benzoylation) is carried out starting at 00°C. up to room temperature.

In the third step the lactone is reduced to a hemiketal. This reductionis effected using a hydride based reduction agent for example usingdiisobutylaluminium-hydride (hereinafter referred to as Dibal-H),preferably in a solvent such as tetrahydrofuran (hereinafter referred toas THF) or toluene. Through this reaction an anomeric centre is created.This reduction is carried out below 0° C., preferably below −60° C., forexample at −78° C.

The fourth step involves two subsequent reactions whereby first theanomeric hydroxyl group is protected prior to deprotection of thehydroxy group on position 3. The anomeric hydroxy group is preferablyprotected with the same protecting group as the hydroxy group onposition 2. For example also with a TBDMS group using TBDMSCI in thepresence of a reactant, preferably imidazole, in an organic solvent, forexample ACN. The base-labile protecting group on position 3 is removedunder the appropriate conditions. For example the O-benzoyl group isremoved with saturated ammonia in methanol. Upon protection of theanomeric hydroxy group, two stereoisomers are formed at that position,alpha and beta. The resulting mixture does not need to be separatedbecause the stereo-orientation of the anomeric centre at this stage inthe line of synthesis does not affect the stereochemistry of the finalcompounds. Deprotection of the hydroxygroup on position 3 does notaffect the stereochemistry of the carbon atom at that same position.

In the next step, step five in scheme 1, the hydroxy group on position 3is phosphonoalkylated using the appropriately protected phosphonoalkylreagent. For example, a phosphonate function is introduced using thetriflate of diisopropylphosphonomethyl alcohol and NaH in THF.Derivatisation of the hydroxygroup on this position does not affect thestereochemical orientation at the carbon atom of that position.Preferably, this phosphonylation reaction is carried out starting at−78° C. up to room temperature.

The sixth step of the synthesis in scheme 1 consists of replacing theprotection groups on the anomeric centre and on position 2 by adifferent one comprising first, a deprotection step and second, aprotection step with the alternative protecting group. In a workingexample an acyl group replaces the silyl protecting group. Preferably,the TBDMS groups are removed by treatment with acid, preferably anaqueous acid solution, for example trifluoroacetic acid (hereinafterreferred to as TFA) in water. Subsequent acylation is done analogous tothe procedure described for step 2 of this synthetic pathway. Preferablythe di-benzoyl ester is formed.

In the next step, the nucleobase is introduced on position 1 of the thusappropriately protected phosphonylated tetrose derivative. Thenucleobases that are optionally N-acyl-protected (uracil, thymine,N⁶-benzoyladenine, N⁴-acetylcytosine) are first silylated, preferablywith TMS using hexamethyldisilane (hereinafter referred to as HMDS) inthe presence of ammoniumsulphate. Using a Lewis acid catalyst,preferably SnCl₄, the nucleobase is coupled with the tetrose moiety. Thepresence of a 2-O-acyl group, preferably the 2-O-benzoyl group, allowsstereoselective introduction in the presence of a Lewis acid of the basemoiety onto the anomeric centre. Using this method, the nucleobase isintroduced at the side opposite to the hydroxy substituent on position2. Preferably, nucleobase introduction is carried out starting at 0° C.up to room temperature.

The eighth step of the synthetic scheme is characterized by thedeprotection of hydroxy on position 2 and (in case of N-acyl protectednucleobases as possibly adenine and cytosine) deprotection of thenucleobase. The 2-O-acyl group and nucleobase protecting benzoyl oracetyl groups are removed in basic conditions. For example, removal ofthese acyl protecting groups is done with saturated ammonia in methanol(yielding compounds 15-18).

In order to obtain the 3′-O-phosphonate tetrose derivatives, the finalstep now is removal of the phosphonate protecting groups by hydrolysis.For example, hydrolysis of the preferable diisopropyl protecting groupsis achieved successfully by treatment with a trimethylsilyl-halogenide(hereinafter referred to as TMSX) (giving 3a-d). Preferably thesecompounds are treated with TMS-bromide (TMSBr) at room temperature in anorganic solvent such as dichloromethane.

In order to obtain the 2′-deoxygenated analogues(3′-O-phosphonate,2′-deoxy tetrose derivatives) the 2′-OH group of 15-17is removed. In case of the adenine, thymine and uracil derivatives, thisis achieved by a mild method involving derivatisation of the hydroxygroup into a thionocarbonate or dithiocarbonate prior to radicalreduction, giving 19-21. An appropriate reaction process is known asBarton deoxygenation where for example the compound is first added to asolution of phenyl(chloro)thiocarbonate in ACN in the presence of acatalytic amount of dimethylaminopyridine (hereinafter referred to asDMAP). Preferably, this first reaction of the barton deoxygenation iscarried out starting at room temperature. The resulting compound is thentreated with tributyltinhydride and 2,2′-Azobisisobutyronitrile(hereinafter referred to as AIBN) in a dry organic solvent for exampledry toluene and allowed to react under reflux. Preferably, this secondreaction of the barton deoxygenation is carried out at refluxtemperature of the solvent used.

The 2′-deoxygenated cytosine derivative is obtained from the2′-deoxygenated uracil derivative. Hereto, the oxygen on position 4 ofthe pyrimidine base is activated by treatment with a mixture of1,2,4-triazole and phosphorus oxychloride in pyridine and subsequentlydisplaced by nitrogen due to treatment with ammonia gas.

The final step in the synthesis of these3′-O-phosphonate,2′-deoxy-tetrose derivatives is the removal of thephosphonate protection groups by hydrolysis. For example, hydrolysis ofthe preferable diisopropyl protecting groups is achieved successfully bytreatment with a TMSX. Preferably, the adenine derivative is treatedwith TMSBr and the thymine, uracil and cytosine derivatives arepreferably treated with TMS-iodine (hereinafter referred to as TMSI).

All the resulting compounds of this synthetic pathway are purified usingone or a combination of several methods known to the person skilled inthe art such as chromatographic methods on conventional silica geland/or ion-exchange columns and/or macroscopic synthetic beads from adextran polymer.

FIG. 2

The synthetic pathway shown in scheme on FIG. 2 illustrates thesynthesis of the 3′-O-phosphonate and 3′-O-phosphonate,2′-deoxy-tetroseguanosine derivatives starting from(R,R)-2,3-dihydroxy-dihydro-furan-1-one.

The phosphonylated and protected tetrose starting material of thispathway is obtained following the steps 1-5 of the synthetic pathwaygiven in FIG. 1.

From there on, similar to the pathway in FIG. 1, the guanosine base isintroduced onto the sugar on position 1 optionally after silylation forexample with HMDS together with ammoniumsulphate. Using a Lewis acidcatalyst, preferably SnCl₄, the nucleobase is coupled with the tetrosemoiety. The presence of a 2-O-acyl group, preferably the 2-O-benzoylgroup, allows stereoselective introduction in the presence of a Lewisacid of the base moiety onto the anomeric centre. Using this method, thenucleobase is introduced at the side opposite to the hydroxy substituenton position 2

Subsequent deprotection of the hydroxy group on position two is achievedin the same way as step 8 of the scheme in FIG. 1.

The final step in order to obtain the 3′-O-phosphonate tetrose guanosinederivative is phosphonate deprotection achieved by hydrolysis. Forexample, hydrolysis of the preferable diisopropyl protecting groups isachieved successfully by treatment with a TMSX, more specifically withTMSBr at room temperature in an organic solvent such as dichloromethane.

In order to obtain the 2′-deoxygenated analogues(3′-O-phosphonate,2′-deoxy tetrose derivatives) the 2′-OH group isremoved in a similar way as for the deoxy compounds of in FIG. 1: by amild method involving derivatisation of the hydroxy group into athionocarbonate or dithiocarbonate prior to radical reduction,preferably using the reaction process that is known as Bartondeoxygenation.

The final step in the synthesis of the 3′-O-phosphonate,2′-deoxyguanosine tetrose derivatives is the removal of the phosphonateprotection groups by hydrolysis. Hydrolysis of the preferablediisopropyl protecting groups is achieved successfully by treatment withTMSI.

The resulting compounds of this synthetic pathway are purified using oneor a combination of several methods known to the person skilled in theart such as chromatographic methods on conventional silica gel, reversedphase silica gel and/or ion-exchange columns and/or macroscopicsynthetic beads from a dextran polymer.

FIG. 3

The reaction scheme given in FIG. 3 comprises 10 steps and illustratesthe synthesis of 3′-O-phosphonate and tetrose derivatives with differentsubstituents on position 2, starting from(R,S)-2,3-dihydroxy-dihydro-furan-1-one.

The first step of the synthesis comprises two reactions that areidentical to the two first steps of the pathway represented by FIG. 1.The second step of the synthesis also comprises two reactions of whichthe first one is identical to step 3 in the pathway of FIG. 1. In thesubsequent reaction, the anomeric hydroxy group is protected, forexample with an alkyl group, for example methyl, by acid catalysedtransacetalisation (for example in methanol when the methyl hemiketal isenvisaged) or using methyl iodide/silver oxide in a polar solvent suchas DMF or ACN.

The next step comprises deprotection on position 3 followed byphosphonylation on position 3. These reactions have been described indetail for the pathway represented by FIG. 1. Deprotection on position 3embraces the removal of the base-labile protecting group. For example,the O-benzoyl group is removed with saturated ammonia in methanol.Subsequently, the phosphonoalkoxy group is introduced on position 3following the same procedures as described for step 5 in the pathway ofFIG. 1.

In the fourth step, three subsequent reactions lead to the coupling ofthe tetrose with the nucleobase. All three reaction-procedures are knownfrom the pathway in FIG. 1, namely the reaction comprised by step 6 and7 of the pathway in FIG. 1. Albeit that the intermediary products(before introduction of the nucleobase) differ with those in FIG. 1 atthe level of derivatisation on position 1. However, the resultingproducts correspond to compounds 11-14 of FIG. 1.

Hence, the first 4 steps of this synthesis pathway can be considered asanother new orthogonal protection strategy in the synthesis of3′-phosphonylated tetrose nucleosides.

In the next step, the acyl protection group on position 2 is removed bya method as described for removal of the same type of protecting groupin step 4 in FIG. 1.

Following the deprotection of the 2′-OH, an oxidation takes place atthis same position in the step 6. The oxidation on position 2 isachieved using one of the many reagents known to the person skilled inthe art to oxidize the 2′ or 3′-hydroxy group of a nucleoside, forinstance chromic acid/acetic anhydride under acidic conditions or aDess-Martin reagent or treament with dimethylsulfoxide (hereinafterreferred to as DMSO) in combination with dicyclohexylcarbodiimide(hereinafter referred to as DCC) under acidic conditions is used.

A novel class of 3′-O-phosphonylated tetrose nucleosides is obtainedwhen removing the phosphonyl protecting groups as described forphosphonyl deprotection in the pathway of FIG. 1.

Alternatively, the oxidation product of step 6, is used for thesynthesis of other derivatives by first introducing a second substituenton position 2 by nucleophilic addition. For the nucleophilic additionreaction, reagent and reaction conditions are chosen appropriate for thedesired substituent. For example, the methyl group is introduced usingmethyllithium/methylbromide magnesium, the trifluoromethyl group isintroduced using trifluoromethyltrimethylsilane (hereinafter referred toas TMSCF₃) in the presence of a catalytic amount oftetra-n-butylammonium fluoride (hereinafter referred to as TBAF) and forexample, the ethinyl group is introduced usingtrimethylsilylethinylbromide magnesium.

The nucleophilic addition reaction proceeds stereospecifically: thenucleophile attacks from the least sterically hindered side and, sincethe bulky substituents on positions 1 and 3 are both on the same side,the nucleophile attacks at the opposite side, resulting in thestereoconformation illustrated by the figure.

Deprotection of the phosphonyl group as described above at this point,leads to 2′-di-substituted analogs. Alternatively, a double bond can beformed by dehydration between position 2 and position 3 prior tophosphonyl deprotection. In a preferred embodiment of the invention thisis achieved by base treatment, for example by treatment with sodiummethanolate (hereinafter referred to as MeONa) in methanol. Though in apreferred embodiment, this is done under aprotic conditions for exampleusing DBU in an aprotic solvent such as dichloromethane (hereinafterreferred to as DCM).

FIG. 4

The reaction scheme given in FIG. 4 illustrates the synthesis of3′-O-phosphonate and tetrose derivatives with different substituents onposition 2 through an alternative pathway. The synthesis of thesecompounds is achieved in 10 steps, starting from(R,S)-2,3-dihydroxy-dihydro-furan-1-one.

The first 5 steps of the pathway in FIG. 4 are identical to the first 5steps of the pathway in FIG. 3 resulting both in the same keyintermediate. The hydroxy on position 2 of this intermediate is replacedby a substituent other than OH by a nucleophilic substitution optionallyafter activation of the hydroxy group as a leaving group. Activation ofthe hydroxy as a good leaving group is preferably done by mesylation,for example by reacting the hydroxygroup with mesylchloride (hereinafterreferred to as MsCl) in a base catalysed environment with for exampleTEA in an organic solvent such as DCM. The (activated) hydroxy group issubstituted by nucleophilic attack resulting in inversion of theconfiguration at that carbon, for example the hydroxy is replaced by anazido group after treatment with sodiumazide. Alternatively a fluorideis introduced on position 2 replacing the hydroxy after reaction withN,N′-diethylaminosulfur trifluoride (DAST) as reagent.

Subsequent phosphonyl deprotection levers the next phosphonylatedtetrose nucleoside.

The conformation of the hydroxy on position 2 of this key-intermediateis also inverted by an oxidation/reduction process. First the compoundis treated by an oxidising agent identical to the ones described forstep 6 in the pathway of FIG. 3. after the oxidation, the compound isreduced again, preferably by treatment with a metal hydride in anorganic solvent for using sodiumborohydride (hereinafter referred to asNaBH₄) example THF or methanol.

The resulting compound of this oxidation/reduction process has acombination of configuration on positions 1, 2 and 3 that is novel.Therefore, in a next step, the remaining protecting groups, being thephosphonyl protecting groups, are removed by the same treatment asdescribed above.

Alternatively, the intermediate resulting from the oxidation/reductionprocess undergoes nucleophilic substitution as described for an earlierstep in this pathway. After, subsequent phosphonyl protecting groupremoval, another set of novel 3′-phosphonylated tetrose nucleosideanalogs is synthesised.

FIG. 5

The reaction scheme given in FIG. 5 illustrates the synthesis of anotherset of 3′-O-phosphonate tetrose nucleoside derivatives with differentsubstituents on position 2 through another pathway. The presentedpathway comprises mostly steps or reactions that were used at some stagein the synthetic pathways of FIGS. 1-4 and which are described above,except for two reactions or steps. Starting with(R,S)-2,3-dihydroxy-dihydro-furan-1-one, the first three steps areidentical to the first three steps in FIG. 3.

In the next step, the first reaction is a new one and is an alternativeway of removal of silylprotecting groups namely a method using afluoride reagent, preferably using ammonium fluoride in THF. The secondreaction in this step is oxidation on position 2 for which the methodhas been described above for FIG. 3. The next step is nucleophilicaddition on position 2 as described for FIG. 3 as well. The resultingproduct is a mixture of two diastereoisomers that are separated based onthe difference of their fysicochemical properties yielding substantiallypure stereoisomers by methods know to the person skilled in the art. Thenucleophilic attack of this nucleophilic addition reaction is notstereospecific because the position is much less sterically hindered dueto the much smaller substituent on position 1.

Next, the free hydroxy group on position 2 is protected by acylation,preferably benzoylation, followed by introduction of the nucleobase onposition 1 and subsequent removal of the all the base-labile protectinggroups, namely the protection of the nucleobase and the protection ofthe hydroxy on position 2. All three of these reactions have beendescribed for steps four and five in FIG. 3.

The resulting compounds are then derivatized in three different ways. Inone possible final step, the phosphonate protecting groups are removedusing the same method as described for phosphonate deprotection in FIG.1.

The second way is characterized by removal of the hydroxy on position 2.This is achieved by a mild method involving derivatization of thehydroxy group into a thionocarbonate or dithiocarbonate prior to radicalreduction. An appropriate reaction process is known as Bartondeoxygenation. Subsequent removal of the phosphonate protecting groupsby the methods described above yields another set of 2′-nuclophilesubstituted derivatives. The third way involves a dehydration step asdescribed for a final step in FIG. 3. In a preferred embodiment of theinvention the dehydration is achieved by base treatment, for example bytreatment with sodium methanolate (hereinafter referred to as MeONa) inmethanol. Though in a preferred embodiment, this is done under aproticconditions for example using DBU in an aprotic solvent such asdichloromethane (hereinafter referred to as DCM).

FIG. 6

The reaction scheme given in FIG. 6 illustrates the synthesis of anotherset of 3′-O-phosphonate tetrose nucleoside derivatives with differentsubstituents on position 2 through another pathway. “Differentsubstituents” should be understood both in terms of different chemicalcomposition as well as the same chemical substituents in a differentstereoconformation. The presented pathway comprises only steps orreactions that were used at some stage in the synthetic pathways ofFIGS. 1-5 and which are described above. This scheme illustrates how theuse of a different stereoisomer of the starting material leads todifferent possibilities for synthesis.

More specifically, the first 6 steps of this synthetic route areidentical to the first 6 steps of the synthetic pathway of FIG. 3.However, due to the fact that the orientation of the nucleobase relativeto the orientation of the substituent on position 3 in the oxidationproduct is different from this relative orientation of the same compoundin FIG. 3, subsequent nucleophilic addition, although performed underthe same conditions, leads to nucleophilic attack from both sides in thepathway of FIG. 6 contrary to the stereoselectivity of this step in FIG.3 (due to steric hindrance). The difference of stereoconfiguration ofthis keyintermediate is due to the different stereoconformation of thestarting material: (S,S)-2,3-dihydroxy-dihydro-furan-1-one. This leadsto the formation of mixture of two diastereoisomers that can beseparated as described above.

FIG. 7

The same accounts for FIG. 7 as for FIG. 6. All the reactions used inthe synthetic pathway of FIG. 7 are already described for the othersynthetic pathways. However, due to the fact that the orientation of thenucleobase relative to the orientation of the substituent on position 3in the oxidation product is different from this relative orientation ofthe same compound in FIG. 3, subsequent nucleophilic substitution,although performed under the same conditions, leads to nucleophilicattack from both sides in the pathway of FIG. 7 contrary to thestereoselectivity of this step in FIG. 4 (due to steric hindrance). Thedifference of stereoconfiguration of this key intermediate is due to thedifferent stereoconformation of the starting material,(S,S)-2,3-dihydroxy-dihydro-furan-1-one. This leads to the formation ofmixture of two diastereoisomers that can be separated as describedabove.

FIG. 8

The reaction scheme given in FIG. 8 illustrates the synthesis of anotherset of 3′-O-phosphonate tetrose nucleoside derivatives with a secondsubstituent on position 3. The pathway comprises 11 steps in total,start with (R,S)-2,3-dihydroxy-dihydro-furan-1-one and results in thesynthesis of 4 end product groups (see boxed structures). The presentedpathway comprises mostly steps or reactions that were used at some stagein the synthetic pathways of FIGS. 1-7 and which are described above butused in a different order (at a different stage of the chronologicalorder of the synthetic pathway) and for some of the reactions to executea modification at a different site of the molecule when compared to theprevious synthetic pathways. For example, the oxidation reaction in step3 of the pathway is carried out under the same conditions as describedabove (see FIG. 3) but is used to oxidize at position 3.

This synthetic pathway therefore very well illustrates thediversification of end products enabled by the reactions described inall FIGS. 1 to 15.

FIG. 9

The reaction scheme given in FIG. 9 illustrates the synthesis of a setof 3′-O-phosphonate tetrose nucleoside derivatives similar to thecompounds resulting from the synthesis in FIG. 8 but with differentstereoconformation due to the use of the same starting material but in adifferent conformation. The starting material is(S,S)-2,3-dihydroxy-dihydro-furan-1-one.

FIG. 10

The reaction scheme given in FIG. 10 illustrates the synthesis of a setof 3′-O-phosphonate tetrose nucleoside derivatives similar to thecompounds resulting from the synthesis in FIG. 5 but with differentstereoconformation due to the use of the same starting material but in adifferent conformation. The starting material is(R,R)-2,3-dihydroxy-dihydro-furan-1-one.

FIG. 11

The reaction scheme given in FIG. 11 illustrates the synthesis of a setof 3′-O-phosphonate tetrose nucleoside derivatives similar to thecompounds resulting from the synthesis in FIG. 6 but with differentstereoconformation due to the use of the same starting material but in adifferent conformation. The starting material is(R,R)-2,3-dihydroxy-dihydro-furan-1-one.

FIG. 12

The reaction scheme given in FIG. 12 illustrates the synthesis of a setof 3′-O-phosphonate tetrose nucleoside derivatives similar to thecompounds resulting from the synthesis in FIG. 7 but with differentstereoconformation due to the use of the same starting material but in adifferent conformation. The starting material is(R,R)-2,3-dihydroxy-dihydro-furan-1-one.

FIG. 13

The reaction scheme in FIG. 13 illustrates the synthesis of a set of3′-O-phosphonate tetrose nucleoside derivatives characterized by theabsence of a substituent other than H on position 2. Although similarcompounds have been synthesized through one of the pathways illustratedby FIGS. 1 to 12, the scheme in FIG. 13 describes an alternative pathwayfor the synthesis of these compounds by using different startingmaterial: starting from β-Hydroxy-γ-butyrolactone which is commerciallyavailable. For the example given in FIG. 13, the stereoisomer(S)-β-Hydroxy-γ-butyrolactone is used.

In the first step, the hydroxyl group in position 3 is protected bybenzoylation (reaction conditions see FIG. 1, step 2). In the secondstep, the lacton is reduced (reaction conditions see FIG. 1, step 3).The anomeric hydroxyl group is protected by acylation, preferablyacetylation for example using acetic acid anhydride in triethylamine asthe solvent and a catalytic amount of DMAP starting at 0° Celsius andallow the reaction to proceed while warming up till room temperature.Subsequently, in the fourth step, the nucleobase is introduced,preferably using SnCl₄ as Lewis catalyst, giving a mixture of twostereoisomers with the base moiety in β and α configurationrespectively. This mixture is separated based on the difference ofphysico-chemical properties of diastereoisomers preferably usingchromatographic techniques for example preparative thin layerchromatography.

In the next step, both compounds undergo deprotection of the hydroxygroup on position 3 using the same procedure as previously describedremoval of base labile-protecting groups for step 4 in FIG. 1. Next, thephosphonate function is introduced using the same procedure as step 5 inFIG. 1. Finally, the phosphonate protection groups are removed and thecompounds purified following the same procedures as previously describedfor the compounds in FIGS. 1-13.

FIG. 14

FIG. 14 exemplifies the synthetic pathway illustrated by FIG. 13 for theadenine derivatives.

FIG. 15

FIG. 15 illustrates a possible way to synthesize the triphosphateanalogue of the of the present invention. Several methods fortransforming a nucleoside monophosphate into a tri-phosphate are knownto the person skilled in the art and all these methods are suitable forintroducing two phosphate groups onto the phosphonyl group of thephosphonoalkyloxytetrose nucleoside analogs of the present invention.Preferably, a diphosphate is introduced onto the phosphonyl group of thephosphonylated tetrose nucleoside derivatives synthesized following oneof the pathways as illustrated by FIGS. 1-14, by first treatment of asolution of the compound in an organic solvent for example DMF, withdimethylformamide dimethyl acetal at room temperature overnight. Aftersubsequent evaporation of the solvent, the residue is dissolved in anorganic solvent again, preferably DMF, and treated withN,N′-carbonyldiimidazole. After 12 h a solution of dibutylammoniumpyrophosphate is added and the mixture is kept at room temperature for 2h. Then the mixture is treated with NH₄OH and subsequently concentratedunder reduced pressure. The resulting phosphonyl-diphosphate is purifiedby methods known to the person skilled in the art, preferably columnchromatography, for example reversed phase chromatography.

General Methods for Antiviral Screening

General methods that can be used for testing the anti-viral activity ofthe compounds of this invention include, but are not limited to, thefollowing:

Anti-HIV Assay:

The inhibitory activity of compounds of the invention can be tested fortheir potential to inhibit the replication of HIV and SIV in a cellculture model for acute infection. Compounds can be tested against HIV-1strains (NL43, III_(B)), HIV-2 strains (ROD, EHO), and SIV (MAC251) forinhibition of virus-induced cytopathicity in MT-4 cells (or CEM or C8166or Molt4/C8 cells), using the colorimetric test described by Pauwels etal. in J. Virol. Methods (1988) 20:309-321 or a microscopicinvestigation of the cytopathogenic effect, evaluation being made 4 to 5days post-infection. For example microtiter 96-well plates containing˜3×10⁵ CEM cells/ml, infected with 100 CCID₅₀ of HIV per ml andcontaining appropriate dilutions of the test compounds can be used. Arapid and automated assay procedure can be used for the in vitroevaluation of anti-HIV agents. An HTLV-1 transformed T4-cell line MT-4,which was previously shown to be highly susceptible to and permissivefor HIV infection, can serve as the target cell line. Inhibition of theHIV-induced cytopathogenic effect is used as the end point. Theviability of both HIV- and mock-infected cells is also assessedspectrophoto-metrically via in situ reduction of3(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT).Methods comprise for example the microscopic examination of CEM, C8166or Molt4/C8 giant (syncytium) cell formation, after 4 to 5 days ofincubation at 37° C. in a CO₂-controlled humidified atmosphere. The 50%cytotoxic concentration (CC₅₀ in μg/ml) is defined as the concentrationof compound that reduces the absorbance of the mock-infected controlsample by 50%. The percent protection achieved by the compound inHIV-infected cells is calculated by the following formula:

$\frac{\left( {OD}_{T} \right)_{HIV} - \left( {OD}_{C} \right)_{HIV}}{\left( {OD}_{C} \right)_{MOCH} - \left( {OD}_{C} \right)_{HIV}}\mspace{14mu} {expressed}\mspace{14mu} {in}\mspace{14mu} \%$

whereby (OD_(T))_(HIV) is the optical density measured with a givenconcentration of the test compound in HIV-infected cells; (OD_(C))_(HIV)is the optical density measured for the control untreated HIV-infectedcells; (OD_(C))_(MOCK) is the optical density measured for the controluntreated mock-infected cells; all optical density values are determinedat 540 nm. The dose achieving 50% protection according to the aboveformula is defined as the 50% inhibitory concentration (IC₅₀ in μg/ml).The ratio of CC₅₀ to IC₅₀ is defined as the selectivity index (SI).Cells: MT-4 cells (Miyoshi et al., 1982) are grown and maintained inRPMI 1640 medium supplemented with 10% heat-inactivated fetal calfserum, 2 mM L-glutamine, 0.1% sodium bicarbonate, and 20 μg ofgentamicin per ml.Viruses: The HIV-1 (IIIB, NL4.3) strain (Adachi et al., 1986) is amolecular clone obtained from the National Institutes of Health(Bethesda, Md.). The HIV-1 strain SO0561945 (RT, K103N; Y181C) is astrain resistant to non-nucleoside reverse transcriptase inhibitors. TheHIV-2 (ROD, EHO) (Barré-Sinoussi et al., 1983) stock is obtained fromculture supernatant of HIV-2 infected cell lines. Mac251 is a SIVstrain.

Cytostatic Activity Assays:

All assays are performed in 96-well microtiter plates. To each well areadded 5-7.5×10⁴ cells and a given amount of the test compound. The cellsare allowed to proliferate for 48 h (murine leukemia L1210) or 72 h(human lymphocyte CEM and Molt4/clone 8) at 37° C. in a humidifiedCO₂-controlled atmosphere. At the end of the incubation period, thecells can be counted in a Coulter counter. The IC₅₀ (50% inhibitoryconcentration) was defined as the concentration of the compound thatreduced the number of cells by 50%.

Anti-BVDV Assay:

Cells and viruses: Madin-Darby Bovine Kidney (MDBK) cells are maintainedin Dulbecco's modified Eagle medium (DMEM) supplemented with BVDV-free5% fetal calf serum (DMEM-FCS) at 37° C. in a humidified, 5% CO₂atmosphere. BVDV-1 (strain PE515) is used to assess the antiviralactivity in MDBK cells. Vero cells (ATCC CCL81) are maintained in MEMmedium supplemented with 10% inactivated calf serum, 1% L-glutamine and0.3% bicarbonate.

96 well cell culture plates are seeded with MDBK cells in DMEM-FCS sothat cells reach 24 hr later confluency. Then medium is removed andserial 5-fold dilutions of the test compounds are added in a totalvolume of 100 ul, after which the virus inoculum (100 ul) can be addedto each well. The virus inoculum used results normally in a greater than90% destruction of the cell monolayer after 5 days incubation at 37° C.Uninfected cells and cells receiving virus without compound can beincluded in each assay plate. After 5 days, medium is removed and 90 μlof DMEM-FCS and 10 ul of MTS/PMS solution (Promega) are added to eachwell. Following a 2 hours incubation period at 37° C., the opticaldensity of the wells is read at 498 nm in a microplate reader. The 50%effective concentration (EC₅₀) value is defined as the concentration ofcompound that protects 50% of the cell monolayer from virus-inducedcytopathic effect.

Anti-HCV Assay/Replicon Assay:

-   Huh-5-2 cells [a cell line with a persistent HCV replicon    I389luc-ubi-neo/NS3-3′/5.1; replicon with firefly    luciferase-ubiquitin-neomycin phosphotransferase fusion protein and    EMCV-IRES driven NS3-5B HCV polyprotein] are cultured in RPMI medium    (Gibco) supplemented with 10% fetal calf serum, 2 mM L-glutamine    (Life Technologies), 1× non-essential amino acids (Life    Technologies); 100 IU/ml penicillin and 100 ug/ml streptomycin and    250 ug/ml G418 (Geneticin, Life Technologies). Cells are seeded at    different densities, particularly in a density of 7000 cells per    well in 96 well View Plate™ (Packard) in medium containing the same    components as described above, except for G418. Cells are then    allowed to adhere and proliferate for 24 hours. At that time,    culture medium is removed and serial dilutions of the test compounds    are added in culture medium lacking G418. Interferon alfa 2a (500    IU) are included as a positive control. Plates are further incubated    at 37° C. and 5% CO₂ for 72 hours. Replication of the HCV replicon    in Huh-5 cells results in luciferase activity in the cells.    Luciferase activity is measured by adding 50 μl of 1× Glo-lysis    buffer (Promega) for 15 minutes followed by 50 μl of the Steady-Glo    Luciferase assay reagent (Promega). Luciferase activity is measured    with a luminometer and the signal in each individual well is    expressed as a percentage of the untreated cultures. Parallel    cultures of Huh-5-2 cells, seeded at a density of 7000 cells/well of    classical 96-well cel culture plates (Becton-Dickinson) are treated    in a similar fashion except that no Glo-lysis buffer or Steady-Glo    Luciferase reagent is added. Instead the density of the culture is    measured by means of the MTS method (Promega).

Anti-Coxsackie Virus Assay:

96-well cell culture plates is seeded with Vero cells in DMEM mediumcontaining 10 fetal calf serum (FCS) so that cells reache confluency 24to 48 hours later. Medium are then removed and serial 5-fold dilutionsof the test compounds are added in a total volume of 100 ul, after whichthe virus inoculum (100 μl) is added to each well. The virus inoculumused results normally in a 90-100% destruction of the cell monolayerafter 5 days incubation at 37° C. Uninfected cells and cells receivingvirus without compound can be included in each asay plate. After 5 days,the medium is removed and 90 μl of DMEM-FCS and 10 μl of MTS/PMSsolution (Promega) is added to each well. Following a 2 hours incubationperiod at 37° C., the optical density of the wells can be read at 498 nmin a microplate reader. The 50% effective concentration (EC50) value isdefined as the concentration of compound that protects 50% of the cellmonolayer from virus-induced cytopathic effect.

Anti-Herpes Simplex Virus, Varicella-Zoster Virus and CytomegalovirusAssays:

The antiviral assays HSV-1, HSV-2, VZV, CMV are based on inhibition ofvirus-induced cytopathicity in HEL cell cultures. Confluent cellcultures in microtiter 96-well plates are inoculated with 100 CCID₅₀ ofvirus, I CCID₅₀ being the virus dose required to infect 50% of the cellcultures. After a 1 hour to 2 hours virus adsorption period, residualvirus is removed, and the cell cultures is incubated in the presence ofvarying compound concentrations of the test compounds. Viralcytopathicity is recorded as soon as it reaches completion in thecontrol virus-infected cell cultures that are not treated with the testcompounds.

Feline Corona Virus Assay:

Feline Crandel kidney cells are seeded in 96-well microtiter plates at24,000 cells/well. Then, 24 hrs later, an appropriate inoculum of FCVcan be added together with 5-fold dilutions of the test compounds. After4 days, a MTS/PMS solution can be added to each well. Following a 90 minincubation period at 37° C., the optical density of the wells can beread at 498 nm in a microplate reader.

SARS Virus Assay:

Vero cells can be seeded in 96-well microtiter plates and grown tillconfluency. Then, an appropriate inoculum of SARS virus able to kill thecell culture (cytopathicity) within 72 hrs can be added together with5-fold dilutions of the test compounds. After 3 days, a MTS/PMS solutioncan be added to each well. Following a 3h incubation period at 37° C.the optical density of the wells can be read at 498 nm in a microplatereader.

Anti-Hepatitis B Virus Assay:

The tetracycline-responsive cell lines HepAD38 are used (Ladner et al.in Antimicrob. Agents Chemother. (1997) 41:1715-1720). These arehepatoma cells that have been stably transfected with a cDNA copy of thepregenomic RNA of wild-type virus. Withdrawal of tetracycline from theculture medium results in the initiation of viral replication. Cells arecultured at 37° C. in a humidified 5% CO₂/air atmosphere in seedingmedium, DMEM/Ham's F12 (50/50) supplemented with 10% by volumeheat-inactivated fetal calf serum, 100 IU/ml penicillin, 50 μg/mlstreptomycin, 100 μg/ml kanamycin, 400 μg/ml G418 and 0.3 μg/mltetracycline. When the assay is started, the cells are seeded in 48-wellplates at a density of 5×10⁵/well. After 2 to 3 days the cultures areinduced for viral production by washing with prewarmed PBS and are fedwith 200 μl assay medium (seeding medium without tetracycline and G418)with or without the antiviral compounds. Medium is changed after 3 days.The antiviral effect is quantified by measuring levels of viral DNA inculture supernatant at day 6 post-induction, by a real time quantitativePCR (Q-PCR). The Q-PCR is performed with 3 μl of culture supernatant ina reaction volume of 25 μl using the TaqMan Universal PCR Master Mix(Applied Biosystems, Branchburg, N.J.) with forward primer (5′-CCG TCTGTG CCT TCT CAT CTG-3′ (SEQ ID NO:1); final concentration: 600 nM),reversed primer (5′-AGT CCA AGA GTY CTC TTA TRY AAG ACC TT-3′ (SEQ IDNO:2); final concentration: 600 nM), and Taqman probe (6-FAM-CCG TGT GCACTT CGC TTC ACC TCT GC-TAMRA (SEQ ID NO:3); final concentration 150 nM).The reaction is analyzed using a SDS 7000 (Applied Biosystems, FosterCity, Calif.). A plasmid containing the full length insert of the HBVgenome is used to prepare the standard curve. The amount of viral DNAproduced in treated cultures is expressed as a percentage of the mocktreated samples. The cytostatic effect of the various compounds isassessed employing the parent hepatoma cell line HepG2. The effect ofthe compounds on exponentially growing HepG2 cells is evaluated by meansof the MTS method (Promega). Briefly, cells are seeded at a density of3000/well (96 well plate) and are allowed to proliferate for 3 days inthe absence or presence of compounds, after which time cell density isdetermined.

Example 1 Materials and General Preparation Methods

For all reactions, analytical grade solvents are used. All moisturesensitive reactions were carried out in oven-dried glassware (135° C.)under a nitrogen atmosphere. Anhydrous THF was refluxed oversodium/benzophenone and distilled. A Varian Unity 500 MHz spectrometerand a 200 MHz Varian Gemini apparatus were used for ¹H NMR and ¹³C NMR.Exact mass measurements were performed on a quadrupole time-of-flightmass spectrometer (Q-T of-2, Micromass, Manchester, UK) equipped with astandard electrospray-ionization (ESI) interface; samples were infusedin i-PrOH/H₂O 1:1 at 3 μL/min. Precoated aluminum sheets (Fluka Silicagel/TLC-cards, 254 nm) were used for TLC; The spots were examined withUV light. Column chromatography was performed on ICN silica gel 63-20060 Å.

The nucleosides (3 a-h) were synthesized starting from(R,R)-2,3-dihydroxy-dihydro-furan-1-one (4) according to FIG. 1. Thehydroxyl group in position 2 can be selectively protected with a TBDMSgroup. The free hydroxyl group of 5 is then protected by benzoylationand the lacton is reduced to the hemiketal using Dibal-H in THF. Theanomeric hydroxyl group is protected with a TBDMS group and theO-benzoyl group is removed with ammonia in methanol. At the stage of 8,the phosphonate function is introduced using the triflate ofdiisopropylphosphonomethyl alcohol and NaH in THF. The two silylprotecting groups of 9 are removed and replaced by benzoyl protectinggroups. The presence of a 2-O-benzoyl group allows selectiveintroduction of the base moiety in the β-configuration. The nucleobases(uracil, thymine, N⁶-benzoyladenine, N⁴-acetylcytosine) are introducedafter silylation and using SnCl₄ as Lewis catalyst. Deprotection of11-14 is done in two steps, first, removal of the benzoyl protectinggroups with ammonia in methanol (yielding 15-18), and, second,hydrolysis of the diisopropyl protecting groups with TMSBr at roomtemperature (giving 3 a-d). In order to obtain the 2′-deoxygenatedanalogues, the 2′-OH group of 15-17 is removed by Bartondeoxygenation,^(16,17) giving 19-21. Compound 22 is obtained from 21.Hydrolysis of the phosphonate ester function of 19 was carried out withTMSBr at room temperature. However, for the compounds 20-22, TMSBrrapidly cleaved the nucleobase from the sugar even at 0° C. For thisreason, TMSI was used for hydrolysis of the(diisopropylphosphono)-methyl group of 20-22. After purification bysilica gel chromatography, sephadex-DEAE A-25 resin and Dowex-sodium ionexchange resin, nucleoside phosphonates acid 3 e-h were obtained.

Conditions for each step of FIG. 1 may be summarized as follows: a)TBDMSCI, imidazole, MeCN b) BzCI, pyridine c) Dibal-H, THF d) Sat. NH₃in MeOH e) Trifluoromethanesulfonate of diisopropylphosphonylmethanol,NaH, THF f) TFA/H₂O g) SnCl₄, MeCN h) 1. φC(S)CI, DMAP, MeCN 2.Bu₃SnH,AIBN i) P(O)Cl₃, 1,2,4-triazole, DCM 2. j) 1. TMSBr, DCM sephadex-DEAE,Dowex-Na⁺ k) 1. TMSI, DCM 2. sephadex-DEAE, Dowex-Na⁺.

Example 2 Preparation of Intermediate Compounds2-O-tributyldimethylsilyl-L-threonolactone (5)

To the solution of (3R,4S)-dihydro-3,4-dihydroxyfuran-2(3H)-one 4 (10.8g, 92 mmol) and imidazole (12.5 g, 184 mmol) in 250 mL MeCN was addedTBDMSCI (31.2 g, 3.17 mmol) at 0° C. in one portion. The reactionmixture was slowly warmed to room temperature and stirred overnight. Thereaction mixture was concentrated. The residue was partitioned betweenH₂O and EtOAc. The organic layer was washed with water and brine, andconcentrated in vacuo. The residue was purified by chromatography on asilica gel column (n-hexane/EtOAC=6:1) to afford 5 (15.2 g, 65.4 mmol,yield 71%) as a colorless solid which was characterized as follows:

¹H NMR (200 MHz, DMSO-d6) bH 0.12 (s, 6H, SiCH₃), 0.90 (s, 9H, CH₃),3.86 (dd, J₁=6.96 Hz, J₂=7.70 Hz, 1H, C(4′)H_(a)), 4.11-4.36 (m, 3H, OH,C(3′)H, C(4′)H_(b)), 5.82 (d, J=5.13 Hz, 1H, C(2′)H);

¹³C NMR (200 MHz, DMSO-d6) δ_(C) −4.93 (SiCH₃), 17.99 (C(CH₃)₃), 25.61(C(CH₃)₃), 69.62 (C-4′), 72.62 (C-2′), 74.59 (C-3′), 174.60 (C-1′);

calcd for C₁₀H₂₀O₄Si₁Na₁ [M+Na]⁺ 255.1028, found 255.1010.

2-O-tributyldimethylsilyl-3-O-benzoyl-L-threonolactone (6)

To the solution of 5 (18.00 g, 77.5 mmol) in 200 mL pyridine was addeddropwise BzCl (11.2 mL, 96.9 mmol) at 0° C. The reaction mixture waswarmed to room temperature and stirred overnight. The reaction mixturewas concentrated and coevaporated with 20 mL toluene two times in vacuo.The residue was partitioned between H₂O (100 mL) and EtOAc (350 mL). Theorganic layer was washed with water and brine, and concentrated invacuo. The residue was purified by chromatography on a silica gel column(n-hexane/EtOAc=8:1) to afford 6 (25.9 g, 77.0 mmol) as a colorlesssolid in 99% yield which was characterized as follows:

¹H NMR (500 MHz, DMSO-d6) δ_(H) 0.14 (d, J₁=13.2, 6H, SiCH₃), 0.87 (s,9H, CH₃), 4.23 (dd, J₁=6.8 Hz, J₂=9.3 Hz, 1H, C(4′) H_(a)), 4.68 (dd,J=7.3 Hz, J₂=9.3 Hz, 1H, C(4′) H_(b)), 4.96 (d, J=6.8 Hz, 1H, C(2′)H),5.48 (dd, J₁=7.3 Hz, J₂=13.0 Hz, 1H, C(3′)H), 7.57-8.01 (m, 5H, Ar—H′);

¹³C NMR (500 MHz, DMSO-d6) δ_(C) −5.16 (SiCH₃), −4.84 (SiCH₃), 17.84(C(CH₃)₃), 25.42 (C(CH₃)₃), 67.20 (C-4′), 71.67 (C-2′), 75.46 (C-3′),128.65 (aroma-C), 128.90 (aroma-C), 129.36 (aroma-C), 133.94 (aroma-C),165.08 (Bz-CO), 172.76 (C-1′);

mass calcd for C₁₇H₂₅O₅Si₁ [M+H]⁺ 337.1471, found 337.1465.

2-O-tributyldimethylsilyl-3-O-benzoyl-L-threose (7)

To the solution of 6 (10.0 g, 29.7 mmol) in 100 mL dry THF was slowlydropwise added 1.0 M diisopropyl aluminiumhydride (37.1 mL, 37.1 mmol)in toluene at −78° C. The reaction mixture was stirred at −78° C., andas soon as the starting material was completely consumed (TLC, 4 to 10hours), methanol (10 mL) was added over a period of 5 minutes in orderto quench the reaction. The cooling bath was removed, 100 mL of a sat.aq. sodium potassium tartrate solution and 200 mL of EtOAc were addedand the mixture stirred vigorously for 3 hours. The organic layer waswashed with water and brine, and concentrated in vacuo. The residue waspurified by chromatography on a silica gel column (n-hexane/EtOAc=8:1)to afford 7 (7.40 g, 21.8 mmol) as a colorless solid in 73% yield, whichwas characterized as follows:

¹H NMR (200 MHz, DMSO-d6) δ_(H) 0.10 (s, 6H, Si—CH₃), 0.87 (s, 9H, CH₃),3.93 (dd, J₁=9.89 Hz, J₂=3.66 Hz, 1H, C(4′)H_(a)), 4.16 (br s, 1H, OH),4.24 (dd, J₁=10.26 Hz, J₂=5.86 Hz, 1H, C(4′)H_(b)), 5.02-5.07 (m, 2H,C(2′)H, C(3′)H), 6.54 (d, J=4.76 Hz, 1H, C(1′)H), 7.51-8.00 (m, 5H,Ar—H);

¹³C NMR (200 MHz, DMSO-d6) δ_(C) −7.39 (SiCH₃), −7.30 (SiCH₃), 15.41(C(CH₃)₃), 23.27 (C(CH₃)₃), 67.06 (C-4′)), 77.14 (C-2′)), 78.87 (C-3′),100.23 (C-1′), 126.58 (aroma-C), 127.09 (aroma-C), 131.40 (aroma-C),163.18 (Bz-CO);

mass calcd for C₁₇H₂₆O₅Si₁Na₁ [M+Na]⁺ 361.1447, found 361.1452.

1α,2-di-O-tributyldimethylsilyl-L-threose (8a) and1β,2-di-O-tributyldimethylsilyl-L-threose (8b)

To the solution of 7 (7.30 g, 21.6 mmol) and imidazole (2.94 g, 43.1mmol) in 100 mL MeCN was added TBDMSCI (0.98 g, 23.8 mmol) at 0° C. inone portion. The reaction mixture was slowly warmed to room temperatureand stirred overnight. The reaction mixture was concentrated. Theresidue was partitioned between H₂O and EtOAc. The organic layer waswashed with water and brine, and concentrated in vacuo. The residue wasdissolved in MeOH saturated with ammonia (100 mL), and the reactionmixture was stirred at room temperature overnight. The mixture wasconcentrated, and the residue was purified by column chromatography(n-hexane:EtOAc, 20:1, 10:1) to give compound 8a (2.22 g, 1.40 mmol) ascolorless oil in 42% yield and 8b (1.00 g, 1.40 mmol) as colorless oilin 19% yield which were characterized as follows.

Compound 8a:

¹H NMR (200 MHz, DMSO-d6) δ_(H) 0.06-0.08 (m, 12H, Si—CH₃), 0.87 (s,18H, CH₃), 3.59-3.65 (m, C(2′)H, 1H,), 3.87-3.99 (m, 3H, C4′ H_(a)C(3′)H, C(4′) H_(b)), 5.00 (d, J=1.1 Hz, C(1′)H), 5.07-5.10 (m, 1H, OH);

¹³C NMR (200 MHz, DMSO-d6) δ_(C) −5.14 (SiCH₃), −4.92 (SiCH₃), −4.65(SiCH₃), −4.38 (SiCH₃), 17.66 (C(CH₃)₃), 17.81 (C(CH₃)₃), 25.61(C(CH₃)₃), 25.73 (C(CH₃)₃), 71.92 (C-4′), 76.66 (C-2′), 85.58 (C-3′),103.91 (C-1′);

mass calcd for C₁₆H₃₆O4Si₂Na₁ 371.2050, found 371.2059.

Compound 8b:

¹H NMR (200 MHz, DMSO-d6) δ_(H) 0.05 (s, 6H, SiCH₃), 0.06 (d, J₁=5.2 Hz,SiCH₃), 0.86 (s, 9H, CH₃), 0.87 (s, 9H, CH₃), 3.41 (dd, J₁=8.0 Hz,J₂=3.7 Hz, C(2′)H); 3.81 (dd, J₁=5.2 Hz, J₂=3.7 Hz, C(3′)H), 3.94-4.07(m, 2H, C(4′)H_(a) C(4′)H_(b)), 5.12-5.15 (m, 2H, OH, C(1′)H);

¹H NMR 200 MHz (DMSO-d6+1D D₂O) δ_(H) 0.02 (s, 6H, SiCH₃), 0.04 (d,J₂=4.4 Hz, SiCH₃), 0.84 (s, 18H, CH₃), 3.39 (dd, J₁=7.7 Hz, J₂=3.6 Hz,C(2′)H); 3.79 (dd, J₁=4.4 Hz, J₂=4.4 Hz, C(3′)H), 3.92-4.07 (m, 2H,C(4′)H_(a) C(4′)H_(b)) 5.10 (d, 1H, J₂=3.6 Hz, C(1′)H);

¹³C NMR (200 MHz, DMSO-d6) δ_(C) −4.95 (SiCH₃), −4.74 (SiCH₃), −4.67(SiCH₃), 17.45 (C(CH₃)₃), 25.64 (C(CH₃)₃), 25.79 (C(CH₃)₃), 70.80(C-4′), 74.17 (C-2′), 79.45 (C-3′), 97.11 (C—I′);

mass calcd for C₁₆H₃₆O₄Si₂Na₁ 371.2050, found 371.2052.

1α,2-di-O-tributyldimethylsilyl-3-O-(diisopropylphosphonomethyl)-L-threose(9a) and1β,2-di-O-tributyldimethylsilyl-3-O-(diisopropylphosphonomethyl)-L-threose(9b)

To a solution of 8a (3.41 g, 9.8 mmol) in dried THF (25 mL) was addedsodium hydride (80% dispersion in mineral oil 0.56 mg, 19.6 mmol) at−78° C. Then the solution of the triflate ofdiisopropylphosphonomethanol (5.80 g, 19.6 mmol) in dried THF (10 mL)was dropwise added, and the reaction mixture was slowly warmed to roomtemperature. The reaction was quenched with sat. NaHCO₃ andconcentrated. The residue was partitioned between H₂O and EtOAc. Theorganic layer was washed with water and brine, and concentrated invacuo. The residue was purified by chromatography on a silica gel column(n-hexane/EtOAC=2:1) to afford 9a (4.75 g, 9.0 mmol, 92%) as colorlessoil which was characterized as follows:

¹H NMR (200 MHz, DMSO-d6) δ_(H) 0.06-0.10 (m, 12H, SiCH₃), 0.86 (s, 9H,C(CH₃)₃), 0.87 (s, 9H, C(CH₃)₃), 1.22-1.26 (m, 12H, C(CH₃)₂), 3.75 (d,J=9.2 Hz, 2H, CH₂), 3.78 (d, J=9.2 Hz, 1H, C(4′)H_(a)), 3.88-3.95 (m,1H, C(3′)H), 3.99 (s, 1H, C(2′)H), 4.10 (dd, J₁=9.2 Hz, J2=8.6 Hz, 1H,C(4′)H_(b)), 4.52-4.68 (m, 2H, CH), 5.02 (s, 1H, C(1′)H);

Exact mass for C₂₃H₅₂O₇P₁Si₂ [M+H]⁺ Calcd. 527.2989, found 527.2988.

The synthesis of 9b started from 8b (2.00 g, 5.7 mmol) and followed thesame procedure as for the synthesis of 9a from 8a resulting in a product(2.7 g, 5.1 mmol, yield 90%) as a colorless oil that which wascharacterized as follows:

¹H NMR (200 MHz, CDCl₃) δ_(H) 0.08-0.11 (m, 12H, SiCH₃), 0.93 (br s,18H, C(CH₃)₃), 1.33 (d, J=6.2 Hz, 12H, C(CH₃)₂), 3.66-3.94 (m, 3H,C(4′)H, PCH₂), 4.02-4.22 (m, 3H, C(2′)H, C(3′)H, C(4′)H_(b)), 4.67-4.83(m, 2H, CH(CH₃)₂), 5.13 (d, J=3.7 Hz, 1H, C(1′)H);

¹H NMR (200 MHz, DMSO-d6) δ_(H) 0.06-0.93 (m, 12H, SiCH₃), 0.87 (s, 18H,C(CH₃)₃), 1.22-1.26 (m, 12H, C(CH₃)₂), 3.58-3.65 (m, 1H, C(4′) H_(a)),3.78 (d, J=9.2 Hz, PCH₂), 3.96-4.08 (m, 3H, C(2′)H, C(3′)H, C(4′)H_(b)), 4.51-4.67 (m, 2H, CH(CH₃)₂), 5.15 (d, J=3.7 Hz, 1H, C(1′)H);

¹³C NMR (200 MHz, DMSO-d6) δ_(C) −5.22 (SiCH₃), −5.07 (SiCH₃), −4.58(SiCH₃), 17.88 (C(CH₃)₃), 23.98 (OCH(CH₃)₂), 25.62 (C(CH₃)₃), 25.71(C(CH₃)₃), 65.12 (d, J_(P,C)=173.6 Hz, PCH2), 68.38 (C-4′), 70.87(OCH(CH₃)2), 70.96 (OCH(CH₃)₂), 78.88 (C-2′), 85.68 (d, J_(P,C)=12.0 Hz,C-3′), 97.3 (C-1′);

mass calcd for C₂₃H₅₂O₇P₁Si₂ [M+H]⁺ 527.2989, found 527.2972.

1α,2-O-benzoyl-3-O-(diisopropylphosphonomethyl)-L-threose (10a) and1β,2-O-benzoyl-3-O-(diisopropylphosphonomethyl)-L-threose (10b)

A solution of 9a (4.25 g, 8.1 mmol) in TFA-H₂O (3:1, 20 mL) was allowedto stand at room temperature for 2 hours. The reaction mixture wasneutralized with saturated NaHCO₃ solution. Then the mixture waspartitioned between the DCM (400 mL) and water (20 mL). The organiclayer was washed with water and brine, dried over MgSO₄, and thenconcentrated in vacuo. The residue was purified by chromatography onsilica gel (DCM:MeOH=20:1) to give3-O-diisopropylphosphonomethyl-L-threose (2.20 g, 7.3 mmol) as acolorless amorphous solid in 92% yield.

To the solution of 3-O-(diisopropylphosphonomethyl)-L-threose (687 mg,2.3 mmol) in 100 mL pyridine was added dropwise BzCI (0.67 g, 5.8 mmol)at 0° C. The reaction mixture was warmed to room temperature and stirredovernight. The reaction mixture was concentrated and coevaporated with20 mL toluene two times in vacuo. The residue was partitioned betweenH₂O (20 mL) and EtOAc (150 mL). The organic layer was washed with waterand brine, and concentrated in vacuo. The residue was purified bychromatography on a silica gel column (n-hexane/EtOAc=1:1) to afford 10aand 10b (1.0 g, 2.0 mmol) as colorless oils in 87% yield which werecharacterized as follows:

Compound 10a:

¹H NMR (200 MHz, DMSO-d6) δ_(H) 1.20-1.26 (m, 12H, C(CH₃)₂), 3.40-4.11(m, 3H, PCH₂, C(4′)H_(a)), 4.40-4.54 (m, 2H, C(3′)H, C(4′)H_(b)),4.56-4.71 (m, 2H, OCH(CH₃)₂), 5.51 (s, 1H, C(2′)H), 6.47 (s, 1H,C(1′)H), 7.43-8.07 (m, 10H, Ar—H);

¹³C NMR (200 MHz, DMSO-d6) δ_(C) 23.82 (CH₃), 64.45 (d, J=155.4 Hz,PCH₂), 70.59 (CH(CH₃)), 73.23 (C-4′), 80.12 (C-2′), 80.30 (C-2′), 99.78(C-1′), 129.04 (aroma-C), 129.83 (aroma-C), 134.14 (aroma-C), 164.61(Bz-CO), 165.07 (Bz-CO);

mass calcd for C₂₅H₃₁O₉P₁Na₁ [M+Na]⁺ 529.1603, found 529.1601.

Example 3 Preparation of Final Compounds1-(N⁶-benzoyladenin-9-yl)-2-O-benzoyl-3-O-(diisopropylphosphonomethyl)-L-threose(11)

To a mixture of 10a (425 mg, 0.83 mmol) and silylated N⁶-benzoyladenine(401 mg, 1.6 mmol) in dry MeCN (30 mL) was dropwise added SnCl₄ (0.3 mL,2.5 mmol) under N₂ at room temperature The reaction mixture was stirredat room temperature for 4 to 5 hours. Then the reaction was quenchedwith saturated NaHCO₃. and concentrated. The residue was partitionedbetween H₂O (20 mL) and EtOAc (100 mL). The organic layer was washedwith water and brine, and concentrated in vacuo. The residue waspurified by chromatography on a silica gel column (DCM/MeOH=40:1) toafford 11 (431 mg, 0.69 mmol) as a colorless amorphous solid in 83%yield which was characterized as follows:

¹H NMR (500 MHz, CDCl₃) δ_(H) 1.31-1.36 (m, 12H, CH₃), 3.94 (dd, J₁=14.0Hz, J₂=8.6 Hz, 1H, PC H_(a)), 4.01 (dd, J₁=14.0 Hz, J₂=8.6 Hz, 1H, PCH_(b)), 4.38 (dd, J₁=11.0 Hz, J₂=4.6 Hz, 1H, C(4′)H_(a)), 4.50-4.52 (m,2H, C(3′)H, C(4′) H_(b)), 4.73-4.80 (m, 2H, OCH), 5.08 (s, 1H, C(2′)H),6.56 (s, 1H, C(1′)H), 7.48-7.65 (m, 6H, Ar—H), 8.02-8.08 (m, 4H, Ar—H),8.50 (s, 1H, Adinie-C(8)-H), 8.82 (s, 1H, Adinie-C(2)-H), 9.07 (br s,1H, NH);

¹³C NMR (500 MHz, CDCl₃) δ_(C) 23.97 (CH₃), 24.01 (CH₃), 24.03 (CH₃),24.06 (CH₃), 65.36 (J_(P,C)=168.9 Hz, PCH₂), 71.45 (POCH), 71.51 (POCH),73.55 (C-4′)), 80.27 (C-2′)), 83.74 (J_(P,C)=9.8 Hz, C-3′), 87.86(C-1′)), 122.72 (A-C(5)), 127.80 (aroma-C), 128.65 (aroma-C), 128.67(aroma-C), 128.86 (aroma-C), 129.93 (aroma-C), 132.31 (aroma-C), 133.99(aroma-C), 141.98 (A-C(8)), 149.45 (A-C(6), 151.59 (A-C(4)), 152.93(A-C(2)), 164.44 (OBz(CO)), 165.17 (NBz(CO));

mass calcd for C₃₀H₃₅N₅O₈P₁ [M+H]⁺624.2223, found 624.2222.

1-(thymin-1-yl)-2-O-benzoyl-3-O-(diisopropylphosphonomethyl)-L-threose(12)

Thymine (0.34 g, 2.7 mmol), ammonia sulfate (10 mg, 0.07 mmol) and 6 mLof HMDS were added to dried flask. The mixture was refluxed overnightunder nitrogen. HDMS was removed in vacuo. To the flask with residue wasadded the solution of compound 10a (0.92 g, 1.8 mmol) in 10 mL of dryMeCN followed by dropwise addition of SnCl₄ (640 μL 5.4 mmol) under N₂at room temperature The reaction mixture was stirred for 4 hours. Thereaction was quenched with sat. aq. NaHCO₃ and concentrated to a smallvolume. The residue was partitioned between H₂O (30 mL) and EtOAc (150mL). The organic layer was washed with water and brine, and concentratedin vacuo. The residue was purified by chromatography on a silica gelcolumn (n-hexane/EtOAc=1:1) to afford 12 (0.76 g, 1.4 mmol) as acolorless amorphous solid in 78% yield which was characterized asfollows:

¹H NMR (200 MHz, CDCl₃) δ_(H) 1.35 (d, J=6.2 Hz, 12H, CH₃), 1.99 (d,J=1.5 Hz, 3H, T-CH₃), 3.86-4.05 (m, 2H, PCH₂), 4.11-4.16 (m, 1H,C(4′)H_(a)), 4.26 (br t, 1H, C(3′)H), 4.40 (d, J=10.6 Hz, 1H, C(4′)H_(b)), 4.70-4.86 (m, 2H, OCH(CH₃)₂), 5.38 (s, 1H, C(2′)H), 6.29 (t,J=2.2 Hz, 1H, C(1′)H), 7.43-7.66 (m, 4H, Ar—H, T-C(6)H), 8.02-8.07 (m,2H, Ar—H), 9.13 (s, 1H, NH);

¹³C NMR (200 MHz, CDCl₃) δ_(C) 12.42 (T-CH3), 23.83 (CH(CH₃)₃), 23.92(CH(CH₃)₃), 64.48 (d, J_(P,C)=168.5 Hz, PCH₂), 71.29 (CH(CH₃)₃), 71.45(CH(CH₃)₃), 72.72 (C-4′), 80.28 (C-2′), 83.70 (J_(P,C)=10.6 Hz, C-3′),89.02 (C-1′), 111.39 (T-C(5)), 128.60 (aroma-C), 129.90 (aroma-C),133.84 (T-C(6), 136.12 (aroma-C), 150.42 (T-C(2), 163.86 (T-C(4), 165.32(Bz-CO);

mass calcd for C₂₃H₃₁N₂O₉P₁ [M+H]⁺ 511.1845, found 511.1831.

1-(uracil-1-yl)-2-O-benzoyl-3-O-(diisopropylphosphonomethyl)-L-threose(13)

Uracil (0.81 g, 7.2 mmol), ammonia sulfate (10 mg, 0.07 mmol) and 20 mLof HMDS were added to dried flask. The mixture was refluxed overnightunder nitrogen. HDMS was removed in vacuo. To the residue was added thesolution of compound 10a (2.43 g, 4.8 mmol) in 50 mL of dry MeCNfollowed by a dropwise addition of SnCl₄ (1.7 mL, 14.4 mmol). Thereaction mixture was stirred for 4 hours. The reaction was quenched withsat. aq. NaHCO₃ and concentrated to small volume. The residue waspartitioned between H₂O (30 mL) and EtOAc (100 mL). The organic layerwas washed with water and brine, and concentrated in vacuo. The residuewas purified by chromatography on a silica gel column (DCM/MeOH=25:1) toafford 13 (2.09 g, 4.2 mmol) as a colorless amorphous solid in 84% whichwas characterized as follows:

¹H NMR (500 MHz, DMSO-d6) δ_(H) 1.23-1.26 (m, 12H, CH₃), 3.97 (d, J=9.0Hz, 2H, PCH₂), 4.16 (dd, J₁=10.7 Hz, J₂=4.2 Hz, 1H, C(4′)H_(a)), 4.36(d, J=10.7 Hz, 1H, C(4′)H_(b)), 4.39-4.40 (m, 1H, C(3′)H), 4.58-4.64 (m,2H, OCH(CH₃)₂), 5.41 (s, 1H, C(2′)H), 5.61 (d, J=8.1 Hz, 1H, U—C(5)H),6.02 (d, J=2.0 Hz, 1H, C(1′)H), 7.55-7.60 (m, 2H, Ar—H), 7.63 (d, J=8.1Hz, 1H, U—C(5)H), 7.70-7.73 (m, 1H, Ar—H), 8.02-8.04 (m, 2H, Ar—H), 11.4(s, 1H, NH);

¹³C NMR (500 MHz, DMSO-d6) δ_(C) 23.74 (CH(CH₃)₃), 23.84 (CH(CH₃)₃),63.10 (d, J_(P,C)=168.5 Hz, PCH₂), 70.53 (CH(CH₃)₃), 72.32 (C-4′), 79.83(C-2′), 82.78 (C-3′), 89.06 (C-1′), 101.91 (U—C(5), 128.95 (aroma-C),129.63 (aroma-C), 134.07 (aroma-C), 140.72 (U—C(6), 150.39 (U—C(2)),163.19 (U—C(4), 164.73 (Bz-CO);

mass calcd for C₂₂H₂₉N₂O₉P₁Na₁ [M+Na]⁺ 519.1508, found 519.1506.

1-(N⁴-acetylcytosin-1-yl)-2-O-benzoyl-3-O-(diisopropylphosphonomethyl)-L-threose(14)

N⁴-Acetylcytosine (0.41 g, 2.7 mmol) and ammonia sulfate (10 mg, 0.07mmol) and 6 mL of HMDS were added to dried flask. The mixture wasrefluxed overnight under nitrogen. HDMS was removed in vacuo. To theresidue was added the solution of compound 10a (0.92 g, 1.8 mmol) in 10mL of dry MeCN followed by a dropwise addition of stannic chloride (640μL 5.4 mmol). The reaction mixture was stirred for 4 hours. The reactionwas quenched with sat. aq. NaHCO₃ and concentrated to small volume. Theresidue was partitioned between H₂O (30 mL) and EtOAc (150 mL). Theorganic layer was washed with water and brine, and concentrated invacuo. The residue was purified by chromatography on a silica gel column(n-hexane/EtOAc=2:1) to afford 14 (0.51 g, 0.94 mmol) as a colorlessamorphous solid in 52% yield which was characterized as follows:

¹H NMR (200 MHz, DMSO-d6) δ_(H) 1.17-1.23 (m, 12H, CH(CH ₃)₂), 2.10 (s,3H, CH₃), 3.80-4.00 (m, 2H, PCH₂), 4.24-4.36 (m, 2H, C(4′)H_(a),C(3′)H), 4.48-4.63 (m, 3H, C(4′) H_(b), OCH(CH₃)₂), 5.44 (s, 1H,C(2′)H), 6.04 (s, 1H, C(1′)H), 7.27 (d, J=7.7 Hz, 1H, C—C(5)H),7.54-7.77 (m, 3H, Ar—H), 8.03-8.07 (m, 3H, Ar_(o)—H, C—C(6)H), 10.95 (s,1H, NH);

¹³C NMR (200 MHz, DMSO-d6) δ_(C) 23.76 (CH(CH₃)₃), 24.39 (Ac-CH₃), 63.77(d, J_(P,C)=166.4 Hz, PCH₂), 70.44 (CH(CH₃)₃), 70.59 (CH(CH₃)₃), 73.56(C-4′), 79.75 (C-3′) 82.83 (d, J_(P,C)=13.7 Hz, C-3′), 90.74 (C-1′),94.74 (C—C(5), 128.86 (aroma-C), 129.14 (aroma-C), 134.07 (aroma-C),129.77 (aroma-C), 134.23 (aroma-C), 145.40 (C—C(6), 154.69 (C—C(2)),162.95 (Bz-CO), 164.77 (C—C(4)); 171.26 (Ac-CO);

mass calcd for C₂₄H₃₃N₃O₉P₁ [M+H]⁺ 538.1954, found 538.1956.

1-(adenin-9-yl)-3-O-(diisopropylphosphonomethyl)-L-threose (15)

A solution of 11 (431 mg, 0.80 mmol) in MeOH saturated with ammonia (100mL) was stirred at room temperature overnight. The mixture wasconcentrated, and the residue was purified by column chromatography(CH₂Cl₂:MeOH=9:1) to give compound 15 (278 mg, 0.67 mmol) as a whitepowder in 84% yield which was characterized as follows:

¹H NMR (500 MHz, DMSO-d6): δ_(H) 1.21-1.26 (m, 12H, CH₃), 3.85-3.94 (m,2H, PCH₂), 4.10-4.13 (m, 2H, C(4′) H_(a), C(3′)H), 4.24-4.27 (m, 1H,C(4′) H_(b)), 4.57-4.63 (m, 3H, CH(CH)₃, C(2′)H), 5.93 (d, J=2.1 Hz, 1H,C(1′)H), 6.05 (br s, 1H, OH), 7.24 (s, 2H, NH2), 8.15 (s, 1H, C(2)H),8.18 (s, 1H, C(8)H);

¹³C NMR (200 MHz, DMSO-d6): δ_(C) 23.82 (CH₃), 63.5 (J_(P,C)=164.6 Hz,PCH₂), 70.41 (OCH), 70.53 (OCH), 71.65 (C-4′), 78.27 (C-2′), 85.62(J_(P,C)=13.6 Hz, C-3′), 89.53 (C-1′), 118.79 (A-C(5), 139.39 (A-C(8)),149.47 (A-C(6), 152.90 (A-C(4)), 156.24 (A-C(2));

mass calcd for C₁₆H₂₇N₅O₆P₁ [M+H]⁺ 416.1699, found 416.1681.

1-(thymin-1-yl)-3-O-(diisopropylphosphonomethyl)-L-threose (16)

A solution of 12 (715 mg, 1.7 mmol) in MeOH saturated with ammonia (100mL) was stirred at room temperature overnight. The mixture wasconcentrated, and the residue was purified by column chromatography(CH₂Cl₂:MeOH=10:1) to give compound 16 (515 mg, 1.2 mmol) as a whitepowder in 71% yield which was characterized as follows:

¹H NMR (200 MHz, CDCl₃) δ_(H) 1.27-1.33 (m, 12H, CH₃), 1.93 (d, J=1.7Hz, 3H, T-CH₃), 3.75 (d, J=8.8 Hz, 2H, PCH₂), 4.13 (br t, 1H, C(3′)H),4.24-4.31 (m, 2H, C(4′)H₂), 4.38 (s, 1H, C(2′)H), 4.61-4.80 (m, 2H,OCH(CH₃)₂), 5.81 (s, 1H, C(1′)H), 7.41 (d, J=1.46 Hz, T-C(6)H), 10.27(br s, 1H, NH);

¹³C NMR (200 MHz, CDCl₃) δ_(C) 2.42 (T-CH3), 23.89 (CH(CH₃)₃), 64.46 (d,J_(P,C)=168.5 Hz, PCH₂), 71.26 (CH(CH₃)₃), 73.54 (C-4′), 78.94 (C-2′),85.33 (d, J_(P,C)=10.6 Hz, C-3′), 93.12 (C-1′), 110.12 (T-C(5)), 136.40(T-C(6), 151.08 (T-C(2)), 164.56 (T-C(4));

mass calcd for C₁₆H₂₈N₂O₈P₁ [M+H]⁺ 407.1583, found 407.1568.

1-(uracil-1-yl)-3-O-(diisopropylphosphonomethyl)-L-threose (17)

A solution of 13 (2.03 g, 4.0 mmol) in MeOH saturated with ammonia (300mL) was stirred at room temperature overnight. The mixture wasconcentrated, and the residue was purified by column chromatography(CH₂Cl₂:MeOH=20:1) to give compound 17 (1.52 g, 3.8 mmol) as a whitepowder in 96% yield which was characterized as follows:

¹H NMR (200 MHz, DMSO-d6): δ_(H) 1.19-1.25 (m, 12H, CH₃), 3.78 (dd,J₁=13.9 Hz, J₂=9.2 Hz, PCH_(a)) 3.85 (dd, J₁=13.9 Hz, J₂=9.2 Hz,PCH_(b)), 3.98-4.28 (m, 4H, C(2′)H, C(3′)H, C(4′)H₂), 4.50-4.66 (m, 2H,CH(CH₃), 5.50 (d, J=8.0 Hz, U—C(5)H), 5.66 (d, J=1.5 Hz, OH), 5.93 (d,J=4.4 Hz, C(1′)H), 7.54 (d, J=8.0 Hz, U—C(6)H);

¹³C NMR (200 MHz, DMSO-d6) δ_(C) 23.70 (CH(CH₃)₃), 23.79 (CH(CH₃)₃),63.29 (d, J_(P,C)=166.3 Hz, PCH₂), 70.34 (CH(CH₃)₃), 70.47 (CH(CH₃)₃),72.29 (C-4′), 77.84 (C-2′), 85.23 (J_(P,C)=10.7 Hz, C-3′), 91.68 (C-1′),101.12 (U—C(5)), 141.12 (U—C(6), 150.72 (U—C(2)), 163.46 (C—C(4));

mass calcd for C₁₅H₂₆N₂O₈P₁ [M+H]⁺ 393.1427, found 393.1425.

1-(cytosin-1-yl)-3-O-(diisopropylphosphonomethyl)-L-threose (18)

A solution of 14 (450 mg, 0.84 mmol) in MeOH saturated with ammonia (100mL) was stirred at room temperature overnight. The mixture wasconcentrated, and the residue was purified by column chromatography(CH₂Cl₂:MeOH=20:1) to give compound 18 (281 mg, 0.72 mmol) as a whitepowder in 86% yield which was characterized as follows:

¹H NMR (200 MHz, DMSO-d6) δ_(H) 1.18-1.25 (m, 12H, CH₃), 3.72 (dd,J₁=13.6 Hz, J₂=8.8 Hz, PCH_(a)) 3.84 (dd, J₁=13.6 Hz, J₂=8.8 Hz,PCH_(b)), 3.95-4.05 (m, 3H, C(2′)H, C(3′)H, C(4′)H_(a)), 4.25 (d, J=9.5Hz, C(4′)H_(b)), 4.48-4.64 (m, 2H, CH(CH₃), 5.65 (d, J=7.6 Hz, C—C(5)H),5.70 (d, J=1.5 Hz, OH), 5.85 (d, J=15.4 Hz, C(1′)H), 7.04 (br s,NH_(a)), 7.14 (br s, NH_(b)), 7.50 (d, J=7.6 Hz, C—C(6)H);

¹³C NMR (200 MHz, DMSO-d6): δ 23.68 (CH(CH₃)₃), 23.78 (CH(CH₃)₃), 64.46(d, J_(P,C)=164.8 Hz, PCH₂), 70.30 (CH(CH₃)₃), 70.42 (CH(CH₃)₃), 72.00(C-4′), 78.19 (C-2′), 85.66 (d, J_(P,C)=12.2 Hz, C-3′), 92.30 (C-1′),93.46 (C—C(5)), 141.63 (C—C(6), 155.47 (C—C(2)), 165.94 (C—C(4));

mass calcd for C₁₅H₂₇N₃O₇P₁ [M+H]⁺ 392.1586, found 392.1577.

1-(adenin-9-yl)-2-deoxy-3-O-(diisopropylphosphonomethyl)-L-threose (19)

To a solution of phenyl(chloro)thiocarbonate (0.25 mL, 1.8 mmol) andDMAP (426 mg, 3.5 mmol) in dried MeCN (25 mL) was added compound 15 (483mg, 1.2 mmol) at room temperature. The reaction mixture was stirred for12 hours. The mixture was concentrated, and the residue was purified bycolumn chromatography (CH₂Cl₂:MeOH/10:1) to give1-(adenin-9-yl)-2-O-phenoxy-thiocarbonyl-3-O-diisopropylphosphonomethyl-L-threoseas a colorless oil. To the solution of1-(adenin-9-yl)-2-O-phenoxythiocarbonyl-3-O-diisopropylphosphono-methyl-L-threosein dried 50 mL of toluene was added tributylinhydride (339 μL, 1.2 mmol)and AIBN (48 mg, 0.3 mmol). The reaction mixture was refluxed for 6hours and concentrated in vacuo. The residue was purified by columnchromatography (CH₂Cl₂:MeOH/10:1) to give compound 19 (110 mg, 0.27mmol) as a colorless oil in 23% yield which was characterized asfollows:

¹H NMR (200 MHz, CDCl₃) δ_(H) 1.27-1.34 (m, 12H, CH₃), 2.54-2.75 (m, 2H,C(2)H₂), 3.62-3.82 (m, 2H, PCH₂), 4.04 (dd, J₁=10.3 Hz, J₂=4.0 Hz, 1H,C(4′)H_(a)), 4.35 (d, J=10.3 Hz, C(4′)H_(b)), 4.43-4.48 (m, 1H, C(3′)H),4.62-4.84 (m, 2H, OCH(CH₃)₂), 6.21 (br s, 2H, NH₂), 6.47 (dd, J₁=7.2 Hz,J₂=2.7 Hz, 1H, C(1′)H), 8.31 (s, 1H, A-C(2)H), 8.33 (s, 1H, A-C(8)H);

¹³C NMR (200 MHz, CDCl₃) δ_(C) 23.89 (CH(CH₃)₃), 38.05 (C-2′), 64.10 (d,J_(P,C)=169.4 Hz, PCH₂), 71.31 (CH(CH₃)₃), 71.46 (CH(CH₃)₃), 73.68(C-4′), 80.49 (d, J_(P,C)=10.7 Hz, C-3′), 83.42 (C-1′), 119.50 (A-C(5)),136.63 (A-C(8)), 149.73 (A-C(6)), 153.07 (A-C(4)), 155.62 (A-C(2));

mass calcd for C₁₆H₂₇N₅O₅P₁ [M+H]⁺ 400.1750, found 400.1740.

1-(thymin-1-yl)-2-deoxy-3-O-(diisopropylphosphonomethyl)-L-threose (20)

This compound was prepared as described for 19, using 16 (450 mg, 1.1mmol) as a starting material. Column chromatographic purification(CH₂Cl₂:MeOH=10:1) gave compound 20 (275 mg, 0.70 mmol) as a colorlessoil in 64% yield which was characterized as follows:

¹H NMR (200 MHz, CDCl₃) δ_(H) 1.31 (d, 6H, CH₃), 1.34 (d, 6H, CH₃), 1.97(d, J=1.1 Hz, 3H, T-CH₃), 2.16 (d, J=15.0 Hz, 1H, C(2′) H_(a)),2.46-2.62 (m, 1H, C(2′) H_(a)), 3.72 (d, J=9.2 Hz, 2H, PCH₂), 3.84 (dd,J=10.6 Hz, J₂=3.7 Hz, 1H, C(4′) H_(a)), 4.29-4.37 (m, 2H, C(4′) H_(b),C(3′)H), 4.66-4.84 (m, 2H, OCH(CH₃)₂), 6.24 (dd, J₁=8.0 Hz, J₂=2.6 Hz,1H, C(1′)H), 7.55 (d, J=1.1 Hz, 1H, T-C(6)H), 8.48 (s, 1H, NH);

¹³C NMR (200 MHz, CDCl₃) δ_(C) 12.45 (T-CH3), 23.92 (CH(CH3)₃), 38.27(C-2′), 63.99 (d, J=169.2 Hz, PCH₂), 71.26 (CH(CH₃)₃, 73.36 (C-4′),80.23 (d, J=10.5 Hz, C-3′), 84.83 (C-1′), 110.72 (T-C(5)), 136.55(T-C(6)), 150.57 (T-C(2)), 163.80 (T-C(4));

mass calcd for C₁₆H₂₇N₂O₇P₁Na₁ [M+Na]⁺ 413.1454, found 413.1447.

1-(uracil-1-yl)-2-deoxy-3-O-(diisopropylphosphonomethyl)-L-threose (21)

This compound was prepared as described for 19, using 17 (1.1 g, 2.8mmol) as a starting material. Column chromatographic purification(CH₂CO₂:MeOH=40:1) gave compound 21 (500 mg, 1.3 mmol) as a colorlessoil, in 46% yield, which was characterized as follows:

¹H NMR (200 MHz, CDCl₃) δ_(H) 1.29-1.34 (m, 12H, CH₃), 2.21 (d, J=15.4,1H, C(2′)H_(a)), 2.44-2.60 (m, 1H, C(2′)H_(b)), 3.69 (d, J=9.2 Hz, 2H,PCH₂), 3.86 (dd, J=10.6 Hz, J₂=3.3 Hz, 1H, C(4′)H_(a)), 4.30-4.38 (m,2H, C(4′)H_(b), C(3′)H), 4.65-4.81 (m, 2H, OCH(CH₃)₂), 5.74 (d, J=8.1Hz, 1H, U—C(5)H), 6.21 (dd, J₁=8.0 Hz, J₂=2.0 Hz, 1H, C(1′)H), 7.71 (d,J=8.0 Hz, 1H, U—C(6)H), 9.16 (s, 1H, NH);

¹³C NMR (200 MHz, CDCl₃) δ_(P) 23.98 (CH(CH₃)₃)), 38.42 (C-2′)), 63.86(d, J_(P,C)=170.7 Hz, PCH₂), 71.26 (CH(CH₃)₃), 71.36 (CH(CH₃)₃), 73.94(C-4′), 80.11 (d, J_(P,C)=11.2 Hz, C-3′), 85.44 (C-1′), 101.95 (U—C(5)),140.92 (U—C(6)), 150.63 (U—C(2)), 163.47 (U—C(4));

mass calcd for C₁₅H₂₆N₂O₇P₁ [M+H]^(+377.1478), found 377.1479.

1-(cytosin-1-yl)-2-deoxy-3-O-(diisopropylphosphonomethyl)-L-threose (22)

To the solution of 1,2,4-triazole (662 mg, 9.6 mmol) in 15 mL pyridinewas added phosphorousoxychloride (223 μL, 2.4 mmol) at room temperature.The mixture was stirred for 10 minutes. Then the solution of 21 (289 mg,0.80 mmol) was added to the mixture. The reaction mixture was stirredfor 4 hours. Then ammonia gas was bubbled in to the reaction mixture for1-3 hours and the reaction mixture was concentrated in vacuo. Theresidue was purified by column chromatography (CH₂Cl₂:MeOH=12:1) to givecompound 22 (220 mg, 0.58 mmol) as a colorless foam, in 73% yield, whichwas characterized as follows:

¹H NMR (200 MHz, CDC₃) δH 1.22-1.30 (m, 12H, CH₃), 2.27 (d, J=15.0, 1H,C(2′)H_(a)), 2.41-2.55 (m, 1H, C(2′)H_(b)), 3.63 (d, J=9.5 Hz, 2H,PCH₂), 3.91 (dd, J₁=10.3, J₂=3.5, 1H, C(4′)H_(a)), 4.22-4.36 (m, 2H,C(4′)H_(b), C(3′)H), 4.56-4.76 (m, 2H, OCH(CH₃)₂), 5.77 (d, J=7.3 Hz,1H, C—C(5)H), 6.17 (dd, J₁=7.3, J₂=1.8, 1H, C(1′)H), 7.67 (d, J=7.3 Hz,1H, C—C(6)H), 8.18 (s, 2H, NH₂);

¹³C NMR (200 MHz, CDCl₃) δ_(C) 23.80 (CH(CH₃)₃), 38.46 (C-2′), 63.66 (d,J_(P,C)=172.2 Hz, PCH₂), 71.48 (CH(CH₃)₃), 71.60 (CH(CH₃)₃), 71.75(CH(CH₃)₃), 74.12 (C-4′), 80.40 (d, J_(P,C)=11.2 Hz, C-3′), 86.68(C-1′), 94.21 (C—C(5)), 141.9 (C—C(6)), 156.58 (C—C(2)), 165.83(C—C(1));

mass calcd for C₁₅H₂₆N₃O₆P₁Na₁ [M+H]⁺ 376.1637, found 376.1638.

1-(adenin-9-yl)-3-O-(phosphonomethyl)-L-threose sodium salt (3a)

To a solution of 15 (220 mg, 0.55 mmol) and Et₃N (1 mL) in DCM (9 mL)was added bromotrimethylsilane (290 μL, 2.2 mmol) at room temperature.The reaction mixture was stirred for 48 hours. The reaction was quenchedwith 1.0 M TEAB solution. The mixture was concentrated, and the residuewas purified by column chromatography (CH₂Cl₂:MeOH/2:1, 1:1, 1:2) togive crude title compound. Purification using sephadex-DEAE A-25 withgradient TEAB solution from 0.01 M to 0.5 M and ion exchanges by theDowex-Na⁺ resin offered 3a (96 mg, 0.25 mmol) as a colorless solid, in45% yield, which was characterized as follows:

¹H NMR (500 MHz, D₂O) δ_(H) 3.54-3.62 (m, 2H, PCH₂), 4.32-4.39 (m, 3H,C(4′)H₂, C(3′)H), 4.82 (dd, J₁=2.4 Hz, J₂=2.0 Hz, 1H, C(2′)H), 6.09 (d,J=2.4 Hz, 1H, C(1′)H), 8.23 (s, 1H, A-C(8)H), 8.45 (s, 1H, A-C(2)H);

¹³C NMR (500 MHz, D₂O): δ_(C) 70.1 (d, J_(P,C)=164.6 Hz, PCH₂), 75.38(C-4′), 80.70 (C-2′), 87.56 (J_(P,C)=9.8 Hz, C-3′), 91.93 (C-1′), 121.21(A-C(5), 143.74 (A-C(8)), 151.49 (A-C(6), 155.48 (A-C(4), 158.30(A-C(2));

³¹P NMR (500 MHz, D₂O): δ_(p) 13.64;

mass calcd for C₁₀H₁₃N₅O₆P₁ [M−H]⁻ 330.0603, found 330.0602.

1-(thymin-1-yl)-3-O-(phosphonomethyl)-L-threose sodium salt (3b)

This compound was prepared as described for 3a, using 16 (220 mg, 0.58mmol) as starting material. Compound 3b (90 mg, 0.24 mmol) was obtainedas a colorless solid in 42% yield, which was characterized as follows:

¹H NMR (500 MHz, D₂O) δ_(H) 1.89 (s, 3H, T-CH₃), 3.60-3.68 (m, 2H,PCH₂), 4.16 (d, J=4.1 Hz, 1H, C(3′)H), 4.24 (dd, J₁=10.7 Hz, J₂=4.1 Hz,1H, C(4′)H_(a)), 4.42 (d, J=10.7 Hz, 1H, C(4′)H_(b)), 4.45 (s, 1H,C(2′)H), 5.85 (d, J=1.2 Hz, 1H, C(1′)H), 7.59-7.60 (m, 1H, T-C(6)H);

¹³C NMR (500 MHz, D₂O): δ_(C) 14.28 (T-CH3), 67.95 (d, J_(P,C)=157.2 Hz,PCH₂), 75.78 (C-4′), 80.17 (C-2′), 87.27 (d, J_(P,C)=11.7 Hz, C-3′),94.22 (C-1′), 113.36 (T-C(5)), 140.66 (T-C(6)), 154.30 (T-C(2)), 169.39(T-C(4));

³¹P NMR (500 MHz, D₂O) δ_(P) 15.68;

mass calcd for C₁₀H₁₄N₂O₈P₁ [M−H]⁻ 321.0488, found 321.0474.

1-(uracil-1-yl)-3-O-(phosphonomethyl)-L-threose sodium salt (3c)

This compound was prepared as described for 3a using 17 (200 mg, 0.53mmol) as a starting material and TBMSBr (200 mL, 2.1 mmol). Compound 3c(93 mg, 0.26 mmol) was obtained as a colorless solid, in 49% yield,which was characterized as follows:

¹H NMR (500 MHz, D₂O) δ_(H) 3.58-3.67 (m, 2H, PCH₂), 4.16 (d, J=3.3 Hz,1H, C(3′)H), 4.26 (dd, J₁=10.7 Hz, J₂=3.9 Hz, 1H, C(4′)H_(a)), 4.45 (d,J=10.7 Hz, 1H, C(4′)H_(b)), 4.47 (s, 1H, C(2′)H), 5.85 (d, J=8.0 Hz, 1H,U—C(5)H), 5.85 (s, 1H, C(1′)H), 7.80 (d, J=8.1 Hz, 1H, U—C(6)H);

¹³C NMR (500 MHz, D₂O) 5c 67.98 (d, J=156.2 Hz, PCH₂), 76.22 (C-4′),80.09 (C-2′), 87.15 (d, J=11.7 Hz, C-3′), 94.63 (C-1′), 104.09 (U—C(5)),145.23 (U—C(6)), 154.26 (U—C(2)), 169.22 (U—C(4));

³¹P NMR (500 MHz, D₂O) δ 15.37;

mass calcd for C₉H₁₂N₂O₈P₁ [M−H]⁻ 307.0331, found 307.0325.

1-(cytosin-1-yl)-3-O-(phosphonomethyl)-L-threose sodium salt (3d)

This compound was prepared as described for 3a, using 18 (150 mg, 0.38mmol) as a starting material. Compound 3d (58 mg, 0.16 mmol) wasobtained as a colorless solid, in 43% yield, which was characterized asfollows:

¹H NMR (500 MHz, D₂O) δ_(H) 3.53-3.62 (m, 2H, PCH₂), 4.15 (d, J=3.7 Hz,1H, C(3′)H), 4.27 (dd, J₁=10.7 Hz, J₂=3.7 Hz, 1H, C(4′)H_(a)), 4.42 (s,1H, C(2′)H), 4.44 (d, J=10.7 Hz, 1H, C(4′)H_(b)), 5.86 (s, 1H, C(1′)H),6.01 (d, J=7.6 Hz, C—C(5)H), 7.77 (d, J=7.6 Hz, C—C(6)H);

¹³C NMR (500 MHz, D₂O) 6c 68.0 (d, J_(P,C)=156.2 Hz, PCH₂), 76.17(C-4′)), 80.13 (C-2′)), 87.27 (d, J_(P,C)=11.8 Hz, C-3′)), 95.16 (C-1′),98.23 (C—C(5)), 145.04 (C—C(6)), 160.06 (C—C(2)), 168.84 (C—C(4));

³¹P NMR (500 MHz, D₂O) δ_(P) 15.28;

mass calcd for C₉H₁₃N₃O₇P₁ [M−H]⁻ 306.0491, found 306.0481.

1-(adenin-1-yl)-2-deoxy-3-O-(phosphonomethyl)-L-threose sodium salt (3e)

This compound was prepared as described for 3a, using 19 (70 mg, 0.23mmol) as a starting material. Compound 3e (38 mg, 0.11 mmol) wasobtained as a colorless solid, in 43% yield, which was characterized asfollows:

¹H NMR (500 MHz, D₂O, 60° C.) δ_(H) 2.63 (dd, J₁=15.5 Hz, J₂=1.3 Hz, 1H,C(2′)H_(a)), 2.75-2.81 (m, 1H, C(2′)H_(b)), 3.55-3.64 (m, 2H, PCH₂),4.09 (dd, J₁=10.0 Hz, J₂=4.0 Hz, 1H, C(4′)H_(a)), 4.33 (d, J=10.0 Hz,1H, C(4′)H_(b)), 4.51 (dd, J₁=5.5 Hz, J₂=4.5 Hz, 1H, C(3′)H), 6.39 (dd,J₁=8.0 Hz, J₂=2.0 Hz, 1H, C(1′)H), 8.22 (s, 1H, C(2)H), 8.49 (s, 1H,C(8)H);

¹³C NMR (500 MHz, D₂O) δ_(C) 39.78 (C-2′), 68.34 (d, J_(P,C)=155.2 Hz,PCH₂), 76.53 (C-4′), 82.79 (d, J_(P,C)=11.9 Hz, C-3′), 86.32 (C—I′),121.13 (A-C(5)), 143.89 (A-C(8)), 151.33 (A-C(6)), 155.25 (A-C(4)),158.18 (A-C(2));

³¹P NMR (500 MHz, D₂O) δ_(P) 154.46;

mass calcd for C₁₀H₁₃N₅O₅P₁ [M−H]⁻ 314.0654, found 314.0632.

1-(thymin-1-yl)-2-deoxy-3-O-(phosphonomethyl)-L-threose sodium salt (3f)

To a solution of 20 (260 mg, 0.67 mmol) and Et₃N (1 mL) in DCM (25 mL)was added iodotrimethysilane (0.73 mL, 5.36 mmol) at 0° C. The reactionmixture was stirred for 2 hours. The reaction was quenched with 1.0 MTEAB solution. The mixture was concentrated, and the residue waspurified by column chromatography (CH₂Cl₂:MeOH/2:1, 1:1, 1:2) to givecrude 3f. Purification using sephadex-DEAE A-25 with gradient TEABsolution from 0.01 M to 0.5 M and ion exchanges by the Dowex-Na⁺ resinoffered 3f (95 mg, 0.27 mmol) as a colorless solid, in 40% yield, whichwas characterized as follows:

¹H NMR (500 MHz, D₂O) δ_(H) 1.91 (s, 3H, T-CH₃), 2.29 (d, J=15.4 Hz, 1H,C(2′)H_(a)), 2.58-2.64 (m, 1H, C(2′)H_(a)), 3.57-3.65 (m, 2H, PCH₂),3.95 (dd, J₁=10.5 Hz, J₂=3.4 Hz, 1H, C(4′)H_(a)), 4.38-4.41 (m, 2H,C(4′)H_(b), C(3′)H), 6.20 (dd, J₁=8.3 Hz, J₂=2.4 Hz, 1H, C(1′)H), 7.78(d, J=1.0 Hz, 1H, T-C(6)H);

¹³C NMR (500 MHz, D₂O) δ_(C) 14.50 (T-CH₃), 39.62 (C-2′), 67.81 (d,J=158.1 Hz, PCH₂), 76.63 (C-4′), 82.66 (d, J=11.3 Hz, C-3′), 88.41(C-1′), 113.94 (T-(C(5)), 141.32 (T-(C(6)), 154.68 (T-(C(2)), 169.51(T-C(4));

³¹P NMR (500 MHz, D₂O) δ_(P) 16.02;

mass calcd for C₁₀H₁₄N₂O₇P₁ [M−H]⁻ 305.0538, found 305.0537.

1-(uracil-1-yl)-2-deoxy-3-O-(phosphonomethyl)-L-threose sodium salt (3g)

This compound was prepared as described for 3f, using 21 (154 mg, 0.41mmol) as a starting material and iodotrimethysilane (0.47 mL, 3.3 mmol).Compound 3g (50 mg, 0.14 mmol) was obtained as a colorless solid, in 34%yield, which was characterized as follows:

¹H NMR (500 MHz, D₂O) δ_(H) 2.31-2.35 (m, 1H, C(2′)H_(a)), 2.57-2.62 (m,1H, C(2′)H_(b)), 3.54-3.62 (m, 2H, PCH₂), 3.97 (dd, J₁=10.5 Hz, J₂=3.7Hz, 1H, C(4′)H_(a)), 4.38-4.40 (m, 1H, C(3′)H), 4.42 (dd, J₁=10.5 Hz,J₂=2.0 Hz, 1H, C(4′) H_(b)), 5.88 (d, J=8.3 Hz, 1H, U—C(5)H), 6.21 (dd,J₁=8.2 Hz, J₂=2.0 Hz, 1H, C(1′)H), 7.99 (d, J=8.2 Hz, 1H, U—C(6)H);

¹³C NMR (500 MHz, D₂O) δ_(C) 39.46 (C-2′)), 67.56 (d, J=156.9 Hz, PCH₂),76.77 (C-4′), 82.31 (d, J=13.8 Hz, C-3′), 88.57 (C-1′), 101.45 (U—C(5)),145.81 (U—C(6), 169.23 (U—C(4));

³¹P NMR (500 MHz, D₂O) δ_(P) 15.72;

mass calcd for C₉H₁₂N₂O₇P₁ [M−H]⁻ 291.0382, found 291.0391.

1-(cytosin-1-yl)-2-deoxy-3-O-(phosphonomethyl)-L-threose sodium salt(3h)

This compound was prepared as described for 3f, using 22 (200 mg, 0.53mmol) as a starting material and iodotrimethysilane (0.6 mL, 4.2 mmol).Compound 3h (130 mg, 0.38 mmol) was obtained as a colorless solid, in73% yield, which was characterized as follows:

¹H NMR (500 MHz, D₂O) δ_(H) 2.32 (d, J=15.3, 1H, C(2′)H_(a)), 2.56-2.61(m, 1H, C(2′)H_(b)), 3.52-3.61 (m, 2H, PCH₂), 4.01 (dd, J₁=10.5 Hz,J₂=3.6 Hz, 1H, C(4′)H_(a)), 4.39-4.40 (m, 1H, C(3′)H), 4.44 (dd,J₁=10.7, J₂=1.7 Hz, C(4′) H_(b)), 6.06 (d, J=7.6 Hz, 1H, C—C(5)H), 6.20(dd, J₁=7.8 Hz, J₂=2.0 Hz, 1H, C(1′)H), 7.95 (d, J=7.6 Hz, 1H, C—C(6)H);

¹³C NMR (500 MHz, D₂O) δ_(C) 37.22 (C-2′), 64.88 (d, J=157.2 Hz, PCH₂),74.37 (C-4′), 79.99 (d, J=11.7 Hz, C-3′), 86.71 (C-1′), 95.99 (C—C(5)),143.02 (C—C(6), 157.56 (C—C(2)), 169.2 3 (C—C(4));

³¹P NMR (500 MHz, D₂O) δ_(P) 15.96;

mass calcd for C₉H₁₃N₃O₆P₁ [M−H]⁻ 290.0535, found 290.0542.

Example 4 Antiviral Activity

Compounds 3 a-h were evaluated for their potential to inhibit thereplication of HIV in a cell culture model for acute infection. TheHIV-1 (III_(B)) virus stock and the HIV-2 (ROD) stock were obtained fromthe culture supernatant of HIV-1 or HIV-2 infected MT-4 cells,respectively. The inhibitory effect of the compounds on HIV-1 and HIV-2replication were monitored by measuring the viability of MT-4 cells 5days after infection. Cytotoxicity of the compounds was determined inparallel by measuring the viability of mock-infected cells on day 5,using a tetrazolium based colorimetric method to determine the number ofviable cells.

PMDTA (abbreviation for compound 3e) shows an IC₅₀ value of 1.0 μg/mLboth against HIV-1 and HIV-2. PMDTT (abbreviation for compound 3f) hasan IC₅₀ value of 2.4 μg/mL against HIV-1 and HIV-2. No cytotoxicity wasobserved for PMDTA nor PMDTT at the highest concentration tested (125μg/mL), giving the compounds a SI of >125 (PMDTA) and >50 (PMDTT) inthese cellular systems. In the cellular test system, both compounds areas active as PMEA and PMPA, and their cytotoxicity is lower.

Example 5

The nucleosides 106a and 106b were synthesized starting from(S)-β-Hydroxy-γ-butyrolactone (FIG. 1). The hydroxyl group in position 3is protected by benzoylation and the lactone is reduced using Dibal-H inTHF. The anomeric hydroxyl group is protected with acetic anhydride inpyridine. The nucleobase (N⁶-benzoyladenine) is introduced using SnCl₄as Lewis catalyst, giving a mixture of compound 104a and 104b with thebase moiety in P and a configuration respectively.

Deprotection of 104a and 104b is done in one step, removing the benzoylprotecting groups with ammonia in methanol. Finally, the phosphonatefunction is introduced using the triflate of diisopropylphosphonomethylalcohol and NaH in THF.

(S)-β-Benzoyloxy-v-butyrolactone (101)

To the solution of (S)-β-Hydroxy-γ-butyrolactone (1.0 g, 9.8 mmol) in 25mL pyridine was added dropwise BzCl (1.4 mL, 12.2 mmol) at 0° C. Thereaction mixture was warmed to room temperature and stirred overnight.The reaction was concentrated and coevaporated with toluene two times invacuo. The residue was partitioned between H₂O (15 mL) and EtOAc (40mL). The organic layer was washed with water and brine, and concentratedin vacuo. The residue was purified by chromatography on a silica gelcolumn (n-hexane/EtOAc=8:1) to afford 101 (1.78 g, 8.6 mmol) as a whitesolid, in 89% yield, which was characterized as follows:

¹H NMR (200 MHz, CDCl₃) δ_(H) 2.76-3.08 (m, 2H, C(2′)H₂), 4.58-4.70 (m,2H, C(4′)H₂), 5.70-5.75 (m, 1H, C(3′)H), 7.49-8.07 (m, 5H, Ar—H);

¹³C NMR (200 MHz, CDCl₃) δ_(H) 33.21 (C-2′), 68.88 (C-4′), 71.73 (C-3′),127.24 (arom-C), 128.43 (C-arom), 132.43 (C-arom), 169.05 (Bz-CO);

mass calcd. for C₁₁H₁₀O₄Na₁ 229.0477, found 229.0435.

3-O-benzovl-2-deoxy-threose (102)

To a solution of 101 (0.780 g, 3.8 mmol) in 13 mL dry THF was slowlydropwise added 1.0 M diisopropyl aluminiumhydride (4.7 mL, 4.7 mmol) intoluene at −78° C. The reaction mixture was stirred at −78° C., and assoon as the starting material was completely consumed (TLC, 2 hours),methanol (2 mL) was slowly added in order to quench the reaction. Thecooling bath was removed, 15 mL of a saturated aqueous sodium potassiumtartrate solution and 25 mL of EtOAc were added and the mixture stirredvigorously for 3 hours. The organic layer was washed with water andbrine, and concentrated under vacuo. The residue was purified bychromatography on a silica gel column (n-hexane/EtOAc=8:2) to afford 102(590 mg, 2.8 mmol) as a colorless oil, in 75% yield, which wascharacterized as follows:

¹H NMR (200 MHz, CDCl₃) δ_(H) 2.30-2.40 (m, 2H, C(2′)H₂), 4.05-4.36 (m,2H, C(4′)H₂), 5.30-5.82 (m, 2H, C(1′+3′)H), 7.40-8.07 (m, 5H, Ar—H);

¹³C NMR (200 MHz, CDCl₃) δ_(H) 71.38, 72.63, 73.94, 74.97, 128.44(arom-C), 129.69 (arom-C), 133.27 (arom-C), 166.44 (Bz-CO);

mass calcd. for C₁₁H₁₂O₄Na₁ [M+Na]⁺ 231.0633, found 231.0629.

1β-O-acetyl-3-O-benzoyl-2-deoxy-threose (103a) and1α-O-acetyl-3-O-benzoyl-2-deoxy-threose (103b)

To the solution of 102 (150 mg, 0.72 mmol) in 6.5 mL Et₃N was addeddropwise (CH3CO)₂O (0.34 mL) and DMAP (8.8 mg, 0.072 mmol) at 0° C. thereaction mixture was warmed to room temperature and stirring for 3hours. Then concentrated under vacuo and the residue was purified bychromatography on a silica gel column (n-hexane/EtOAc=9:1) to givecompound 103a (117 mg, 0.47 mmol) as colorless oil, in 65% yield, and103b (32 mg, 0.13 mmole) as colorless oil, in 18% yield, which werecharacterized as follows:

Compound 103a:

¹H NMR (200 MHz, CDCl₃) δ_(H) 2.07 (s, 3H, CH₃), 2.48-2.52 (m, 2H,C(2′)H₂), 4.14 (dd, J₁=10.6 Hz, J₂=2.2 Hz, 1H, C(4′)H_(b)), 4.26 (dd,J₁=10.6 Hz, J₂=4.2 Hz, 1H, C(4′)H_(a)), 5.61-5.65 (m, 1H, C(3′)H), 6.49(t, J=4.0 Hz, 1H, C(1′)H), 7.40-8.05 (m, 5H, Ar—H).

Compound 103b:

¹H NMR (200 MHz, CDCl₃) δ_(H) 2.07 (s, 3H, CH₃), 2.41-2.46 (m, 2H,C(2′)H₂), 4.22 (dd, J₁=10.6 Hz, J₂=2.6 Hz, 1H, C(4′)H_(b)), 4.36 (dd,J₁=10.6 Hz, J₂=5.2 Hz, 1H, C(4′)H_(a)), 5.61-5.65 (m, 1H, C(3′)H), 6.40(d, J=4.4 Hz, 1H, C(1′)H), 7.43-8.09 (m, 5H, Ar—H).

1β-(N⁶-benzoyladenin-9-yl)-3-O-benzoyl-2-deoxy-threose (104a) and1α-(N⁶-benzoyladenin-9-yl)-3-O-benzoyl-2-deoxy-threose (104b)

To a mixture of 103 (210 mg, 0.84 mmol) and N⁶-benzoyladenine (405 mg,1.62 mmol) in dry MeCN (30 mL) was dropwise added SnCl₄ (0.3 mL, 2.5mmol) under N₂ at 0° C. The reaction mixture was warmed to roomtemperature and stirred for 1.5 hours. Then the reaction was quenchedwith sat NHCO₃ and concentrated. The residue was partitioned between H₂O(20 mL) and EtOAc (100 mL). The organic layer was washed with water andbrine and concentrated under vacuum. The residue was purified bychromatography on a silica gel column (CH2Cl2:MeOH/40:0.5) to afford amixture of β/α isomers (187 mg, 0.44 mmol) in 52% yield which werefinally separated using preparative TLC and as eluent (CH₂Cl₂:MeOH/40:1)(3 times), which were characterized as follows:

Compound 104a:

H NMR (500 MHz, CDCl₃) δ_(H) 2.84-2.89 (m, 1H, C(2′)H_(b)), 3.23-3.28(m, 1H, C(2′)H_(a)), 4.29 (d, J=10.6 Hz, 1H, C(4′)H_(b)), 4.63 (dd,J₁=4.3, J₂=10.6 Hz, 1H, C(4′)H_(a)), 5.92 (m, 1H, C(3′)H), 6.50 (t,J=6.5 Hz, 1H, C(1′)H), 7.45-8.15 (m, 10H, Ar—H);

¹³C NMR (500 MHz, CDCl₃) δ_(H) 38.59 (C-2′), 73.43 (C-4′), 74.34 (C-3′),85.15 (C-1′), 127.88 (arom-C), 128.45 (arom-C), 128.73 (arom-C), 129.64(arom-C), 132.69 (arom-C), 133.40 (arom-C), 164.74 (Bz-CO), 166.00(Bz-CO);

mass calcd. for C₂₃H₁₉N₅O₄Na₁ 452.1335, found 452.1339.

Compound 104b:

¹H NMR (500 MHz, CDCl₃) δ_(H) 2.90-2.96 (m, 1H, C(2′)H_(b)), 3.05 (d,J=15.4 Hz, 1H, C(2′)H_(a)), 4.40 (dd, J₁=4.4 Hz, J₂=10.0 Hz, 1H,C(4′)H_(b)), 4.46 (d, J=10.0 Hz, 1H, C(4′)H_(a)), 5.74 (m, 1H, C(3′)H),6.56 (d, J=7.1 Hz, 1H, C(1′)H), 7.38-8.03 (m, 10H, Ar—H);

¹³C NMR (500 MHz, CDCl₃) δ_(H) 38.63 (C-2′), 73.45 (C-3′), 74.80 (C-4′),85.19 (C-1′), 127.90 (arom-C), 128.59 (arom-C), 128.76 (arom-C), 129.36(arom-C), 132.69 (arom-C), 133.54 (arom-C), 164.67 (Bz-CO), 165.79(Bz-CO);

mass calcd. for C₂₃H₁₉N₅O₄Na 1452.1335, found 452.1334.

1β-(adenin-9-yl)-2-deoxy-threose (105a) and1α-(adenin-9-yl)-2-deoxy-threose (105b)

A solution of 104a (90 mg, 0.21 mmol) in methanol saturated withammonium (26 mL) was stirred at room temperature overnight. The solutionwas concentrated under vacuum and the residue was purified by columnchromatography (CH₂Cl₂: MeOH/9:1) to give compound 105a (40 mg, 0.18mmol) as a white solid, in 86% yield, which was characterized asfollows:

¹H NMR (200 MHz, DMSO-d₆) δ_(H) 2.27-2.34 (m, 1H, C(2′)H_(b)), 2.78-2.85(m, 1H, C(2′)H_(a)), 3.76 (d, J=8.8 Hz, 1H, C(4′)H_(b)), 4.21 (dd,J₁=3.6, J₂=8.8 Hz, 1H, C(4′)H_(a)), 4.62 (bs, 1H, OH), 5.20 (d, J=3.6Hz, 1H, C(3′)H), 6.37 (t, J=8.6 Hz, 1H, C(1′)H), 7.26 (bs, 2H, NH₂),8.14 (s, 1H, H-8), 8.30 (s, 1H, H-2).

Compound 105b was prepared as described for 105a using 104b (110 mg,0.26 mmol) as starting material and was obtained (48 mg, 0.22 mmol) as awhite solid in 86% yield, which was characterized as follows:

¹H NMR (200 MHz, DMSO-d₆) δ_(H) 2.23-2.30 (m, 1H, C(2′)H_(b)), 2.63-2.71(m, 1H, C(2′)H_(a)), 3.90-3.93 (m, 2H, C(4′)H₂), 4.45 (m, 1H, OH), 5.80(d, J=4.4 Hz, 1H, C(3′)H), 6.26 (dd, J₁=2.2 Hz, J₂=8.0 Hz, 1H, C(1′)H),7.28 (s, 2H, NH₂), 8.13 (s, 1H, H-8), 8.35 (s, 1H, H-2);

¹³C NMR (200 MHz, DMSO-d₆) δ_(H) 38.49 (C-2′), 66.99 (C-3′), 74.04(C-4′), 80.90 (C-1′), 137.54 (C-8), 150.19 (C-2), 153.90 (C-6).

1β-(adenine-9-yl)-3-(diisopropylphosphonomethyl)-threose (106a) and1α-(adenine-9-yl)-3-(diisopropylphosphonomethyl)-threose (106b)

To the solution of 105a (50 mg, 0.23 mmol) in 5 mL THF, which was cooledusing dry-ice and acetone, was added sodium hydride 80% (11.4 mg, 0.46mmol). The mixture was stirred for 10 min and the solution ofthrifluorate phosphonate (136 mg, 0.46 mmol) in THF was slowly droppedto the reaction flask. Then the mixture was slowly warm to roomtemperature. The reaction was quenched with sat. NaHCO₃ andconcentrated. The residue was partitioned between H₂O and CH₂Cl₂. Theorganic layer was washed with water and brine, and concentrated invacuo. The residue was purified by chromatography on a silica gel column(CH₂Cl₂/MeOH=98:2) to afford 106a as a white solid. Compound 106b wasprepared as described for 106a using 105b as starting material and wasobtained as a white solid, which was characterized as follows:

¹H NMR (200 MHz, CDCl₃) δ_(H) 1.25-1.35 (m, 12H, CH₃), 2.57-2.62 (m, 2H,C(2′)H₂), 3.70 (dd, J₁=1.4 Hz, J₂=8.8 Hz, 2H, PCH₂), 4.04 (dd, J₁=4.2Hz, J₂=10.4 Hz, C(4′)H_(a)), 4.37 (d, J=10.4 Hz, C(4′)H_(b)), 4.47 (m,1H, C(3′)H, 4.71-4.78 (m, 2H, OCH(CH₃)₂), 5.75 (m, 2H, NH₂), 6.47 (dd,J₁=2.7 Hz, J₂=7.0 Hz, C(1′)H), 8.29 (s, 1H, H-8), 8.34 (s, 1H, H-2).

Example 6 Incorporation of PMDTA into DNA Using Reverse Transcriptase

The antiviral activity of the phosphonate nucleosides of the inventionmay be mostly explained by their intracellular metabolisation into theirdiphosphates (hereinafter referred as pp) followed by incorporation intothe viral genome and chain termination. We used a primer/extension assayin order to compare the ability of the HIV reverse transcriptase and thehuman DNA polymerase-α to accept PMDTApp (see FIG. 15) as a substrate incomparison to deoxy-adenosine triphosphate (hereinafter referred asdATP). This will provide us with suitable information about theselectivity of the anti-HIV compound of the invention since the humanDNA polymerase-α is mainly involved in replication of the nuclear genomewhile the HIV reverse transcriptase plays a key role in the replicationof the viral genome.

The following incorporation study was effected with a DNA template and aDNA primer, as DNA polymerase-α and reverse transcriptase are both ableto synthesize double stranded DNA (although reverse transcriptase isalso able to synthesize a DNA strand using RNA as template). Bothenzymes were able to extend a DNA primer with the phosphonatenucleotide, but the modified nucleotide was only a very poor substratefor the human DNA polymerase α. Only a high enzyme concentration (0.4U/μL) resulted in the incorporation of PMDTApp, i.e. a concentrationmore than 100 times higher than the concentration used to incorporatethe natural dATP substrate.

The HIV reverse transcriptase, on the other hand, accepted PMDTApp aseasily as the natural building block. These results fromprimer/extension assays were confirmed by the following kinetic data.

Determination of K_(m) and K_(cat) values for the incorporation of dATPand PMDTApp in a DNA hybrid was carried out under steady-stateconditions as described by Creighton et al. in Methods in Enzymology(1995) 262:232-256. For each determination eight different substrateconcentrations in the range of 0.1 to 12.5 μM were used. Results givenbelow are the average of three independent determinations. The reactionmixture contained 250 nM primer/template complex 0.025 U/μL HIV reversetranscriptase, and the triphosphate nucleotides to be incorporated (dATPand PMDTApp, respectively). The template sequence and the primersequence used in this experiment are shown below. The reaction wasquenched after 1, 2 and 3 minutes by adding a double volume of stopsolution (90% formamide, 0.05% bromophenol blue, 0.05% xylene cyanol and50 mM EDTA). Samples were analyzed by gel electrophoresis on a 16%polyacrylamide ureum gel in TBE buffer (89 mM Tris-borate, 2 mM EDTAbuffer, pH 8.3) after heating the samples for 5 minutes at 70° C.Products were visualised by phosphorimaging. The amount of radioactivityin the bands corresponding to the products of the enzymatic reactionswas determined using the Optiquant Image Analysis Software (Packard).Rate profiles were determined using GraphPad Prism® software.

Results of this experiment are shown in the Table below. These datashow, for the incorporation of PMDTApp by the HIV reverse transcriptase,a small increase in K_(m) value but also a slight increase in k_(cat)value, compared to dATP. This indicates that, although the affinity ofthe enzyme for the phosphonate nucleotide of the invention might beslightly lower, the overall catalytic efficiency differs only with afactor of 2.5.

Since PMDTApp was such a poor substrate for the DNA polymerase-α,kinetic parameters could not be determined under steady-stateconditions.

+dATP or PMDTApp P1 5′ CAGGAAACAGCTATGAC 3′ → (SEQ ID NO: 4) T1 3′GTCCTTTGTCGATACTGTCCCC 5′ (SEQ ID NO: 5)

TABLE Km (in μM) Kcat (in min−1) Kcat/km (in min⁻¹, M⁻¹) dATP 0.10 0.666.6 PMDTApp 0.29 0.79 2.72

These data show that PMDTA can be incorporated into DNA, functioning asa chain terminator. A model was then built in order to analyseinteractions between the incorporated nucleotide and reversetranscriptase. Therefore the adenine phosphonate nucleoside was built atthe 3′-end of the primer and paired with a thymidine nucleotide in thetemplate strand. This model revealed that the sugar ring is puckered inthe C3′-endo conformation. Hydrophobic interactions between thephosphonate nucleotide and reverse transcriptase are occurring at Leu74,Tyr115 and Gln151, while no steric hindrance with Met184 is expected tooccur during translocation. This model visualizes the experimentalresults of the incorporation study of PMDTA into DNA using reversetranscriptase.

1. A process for preparing a compound represented by the general formula(II):

wherein: X¹, X², X³, X⁴ and X⁵ are each —O—, B is selected from thegroup consisting of adeninyl, thyminyl, uracilyl, cytosinyl andguaninyl, R¹ and R² are each independently selected from the groupconsisting of hydrogen, alkyl and P(O)(OH)—O—PO₃H₂, provided that whenone of R¹ and R² is P(O)(OH)—O—PO₃H₂, the other one is hydrogen; R⁴ andR⁵ are each independently selected from the group consisting of hydrogenand OR¹⁴; R³, R⁶, R⁷ and R⁸ are each hydrogen; R¹⁴ is hydrogen orarylalkyl; and n is an integer representing the number of methylenegroups between X₂ and P, and is selected from 1, 2, 3, 4, 5 and 6; or apharmaceutically acceptable salt thereof, the process comprising thestep of coupling a nucleobase B selected from the group consisting ofadenine, thymine, uracil, cytosine and guanine, in the presence of aLewis acid catalyst, with a precursor represented by the general formula

wherein X¹, X², X³, X⁴, X⁵, R¹, R², R³, R⁴, R⁵, R⁶, R⁷, R⁸, R¹⁴ and nare as defined in formula (II) and wherein R⁹ is an O-acyl group.
 2. Theprocess of claim 1, wherein R⁹ is an O-benzoyl group.
 3. The process ofclaim 1, wherein the Lewis acid catalyst is SnCl₄.
 4. The process ofclaim 1, further comprising a step of N-protecting the nucleobase withan acyl group prior to the coupling step.
 5. The process of claim 4,wherein the acyl group is a benzoyl group or an acetyl group.
 6. Theprocess of claim 1, wherein the coupling step is carried out from 0° C.to room temperature.
 7. The process of claim 1, further comprising astep of silylating the nucleobase prior to the coupling step.
 8. Theprocess of claim 7, wherein silylating is performed withhexamethyldisilane.
 9. The process of claim 8, wherein silylating isperformed in the presence of ammonium sulphate.
 10. The process of claim1, wherein R⁵ is OR¹⁴ and R¹⁴ is hydrogen, further comprising a step ofselectively protecting R⁵ prior to the coupling step.
 11. The process ofclaim 1, wherein R¹ and R² are each isopropyl.
 12. The process of claim1, wherein R¹⁴ is benzyl.
 13. The process of claim 1, wherein n is 1.14. The process of claim 11, wherein R¹⁴ is benzyl.
 15. The process ofclaim 11, wherein n is
 1. 16. The process of claim 12, wherein n is 1.17. The process of claim 4, further comprising a step of deprotectingthe nucleobase after the coupling step, said deprotecting step beingperformed under basic conditions.
 18. The process of claim 17, whereinsaid deprotecting step is performed with saturated ammonia in methanol.19. The process of claim 1, wherein R¹ and R² are each hydrogen, furthercomprising a final hydrolysis step.
 20. The process of claim 19, whereinsaid final hydrolysis step is performed by treatment with atrimethylsilyl halogenide.